Why has my Windows Defender stopped working?

FIX: Can't Turn on Windows Defender

Written by Rimvydas Iliavicius on February 22, 2018

• Introduction
• Table Of Contents
• Video Instructions

How to Turn on Windows Defender on Windows 10

Windows Defender is an antivirus program and a fully integrated part of Windows 10. Sometimes, Windows Defender could become disabled, but this article will show you how to turn it back on.

Windows Defender runs in the background, but you can 'snooze' it if you do not wish to be interrupted. You can also scan individual files or do full scans. Windows Defender also scans new drives connected to your computer. If you are running the latest Windows 10 version, you have capable protection set with various useful tools and minimal impact on system performance.

Windows 10 disables Windows Defender if you install a third-party antivirus program. However, it may get disabled by malware, software conflicts, corrupted Windows registry, and so on. In this guide, we present several possible solutions to this problem so that you can turn on Windows Defender.

Video Showing How to Fix Windows Defender if It's Not Turning on:

Table of Contents:

• Introduction
• Restart Windows Security Center Service
• Uninstall Third-Party Antivirus Software
• Update Windows
• Run the SFC Scan
• Perform a Clean Boot
• Scan Your Computer for Malware
• Video Showing How to Fix Windows Defender if It's Not Turning on

Download Computer Malware Repair Tool

It is recommended to run a free scan with Combo Cleaner - a tool to detect malware and fix computer errors. You will need to purchase the full version to remove infections and eliminate computer errors. Free trial available. Combo Cleaner is owned and operated by Rcs Lt, the parent company of PCRisk.com read more.

Restart Windows Security Center Service

Windows Services [also known as services.msc] modify how Windows services run on your system. These services are responsible for running available programs and managing many system settings and resources. You can change a service's settings for security, troubleshooting, and performance-related reasons.

You need to access Windows Services to stop the Security Center service. Windows Security Center service monitors and reports security health settings on the system. The health settings include firewall, antivirus, anti-spyware, Windows Update, and Internet settings.

To restart this service, type "run" in Search and click the "Run" result.

In the Run dialog box, type "services.msc" and click "OK" to open Windows Services.

In the Services window, find the "Security Center" service and right-click on it. Select "Restart" from the drop-down menu.

Another way to restart the Windows Security Center service is to select "Properties" in the drop-down menu when right-clicking on this service. In the Properties windows, find and click "Stop". Wait a few seconds until the service has stopped, click "Start", and it will be started again.

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Uninstall Third-Party Antivirus Software

If any third-party antivirus software is installed on the Windows operating system, Windows Defender will probably detect it and shut itself down. It is usual practice to have multiple security software packages installed on a system, creating conflict between them.

Therefore, consider uninstalling any third-party antivirus software if you want Windows Defender to work properly. After you have uninstalled third-party antivirus software, type "windows defender" in Search and select the "Windows Defender settings" result.

In the Windows Defender settings window, click "Open Windows Defender Security Center".

Now, click "Virus & threat protection".

Click "Virus & threat protection settings".

Ensure that "Real-time protection" is on - this locates and stops malware from installing or running on your device. If turned off, toggle the switch to the "On" position to turn it on.

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Update Windows

You can also try to update the current version of Windows installed on your system. Checking for updates for the entire Windows operating system might also help. An outdated Windows operating system could cause the Windows Defender issue [not being able to turn it on].

Latest signature updates are necessary for Windows Defender to keep your computer secure. Try checking for Windows Updates and then also update Windows Defender itself. To update Windows, type "windows update" in Search and click the "Check for updates" result.

Now, click "Check for updates". If there are any updates available, install them. If any updates are pending [as in our example], click "Restart now" - Windows will restart the computer and install the updates.

When the Windows update process has finished, update Windows Defender. To do this, type "virus" in Search and click the "Virus & threat protection" result.

Now click "Protection updates".

Finally, click "Check for updates". See if this solves the issue of not being able to turn Windows Defender on.

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Run the SFC Scan

System File Checker [SFC] is a utility in Windows that allows users to scan for corruptions in Windows system files and restore them.

To run it, first open Command Prompt first by typing "command prompt" in Search, right-click on "Command Prompt", and then select "Run as administrator" from the drop-down menu to run Command Prompt with administrator privileges.

You must run an elevated Command Prompt to be able to perform an SFC scan.

In opened Command Prompt window, type "sfc /scannow" and press Enter on your keyboard to execute this command. System File Checker will start and take some time to complete the scan [about 15 minutes].

Wait for the scanning process to complete and restart your computer to see if you still have issues turning Windows Defender on.

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Perform a Clean Boot

When you start Windows using a normal start-up operation, several applications and services start automatically and then run in the background. These programs include basic system processes, antivirus software, system utility applications, and other previously installed software.

These applications and services can cause software conflicts. A clean boot is performed to start Windows by using a minimal set of drivers and start-up programs. This helps eliminate software conflicts that occur when installing a program or an update or when running a program in Windows.

To perform a clean boot, type "system configuration" in Search and click the "System Configuration" result.

In the System Configuration window, click the "Services" tab and mark the "Hide all Microsoft services" checkbox. Click on "Disable all".

Then, click the "Startup" tab and click "Open Task Manager".

Under the Task Manager Startup tab, select the first application and click "Disable" to disable it - disable all applications one by one, repeating this step. Once you have disabled all programs, close Task Manager and click "OK" in the System Configuration Startup tab and restart the computer.

Check to see if this fixes the issue with not being able to turn Windows Defender on.

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Scan Your Computer for Malware

There might be malware infections on the system and causing Windows Defender issues. We suggest you scan the system for viruses and see if this solves the problem. Some malware removal tools are detailed below. You will need to start your computer in Safe Mode to successfully scan the system.

Safe Mode is a diagnostic start-up mode in Windows operating systems used to obtain limited access to Windows when the operating system does not start or function normally. It is the reverse of 'Normal Mode', which starts Windows in the usual manner.

One of the most common steps to take when troubleshooting a system is to boot into Safe Mode. Safe Mode starts Windows in a basic state, using a limited set of files and drivers. It can help to troubleshoot problems on your computer. Read this article to find out how to start a computer in Safe Mode.

Use one of these malware removal tools to scan your Windows operating system for possible infections:

Microsoft Safety Scanner

Microsoft Safety Scanner is a free downloadable security tool that provides on-demand scanning and helps to remove viruses, spyware, and other malicious software. You can download it here.

Malwarebytes

Malwarebytes offers a 14-day trial of their Premium edition, providing Real-Time Protection and acting as a full antivirus suite. Malwarebytes claims that they built their product to be compatible with other antivirus software, including Windows Defender. You can download Malwarebytes here.

Emsisoft Emergency Kit

Emsisoft Emergency Kit is another free on-demand scanner that is portable. This means you can store it on a USB drive and scan a system offline. You can download Emsisoft Emergency Kit here.

Zemana Anti-malware

Zemana Anti-Malware is an effective malware detection and removal software that protects users from malware, spyware, adware, ransomware, rootkits, and bootkits. You can download Zemana Anti-Malware here.

We hope that one of the above solutions solves the problem of not turning on Windows Defender. As well as the above methods, you could also simply restart your computer. Sometimes a simple restart can solve the issue.

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About the author:

Rimvydas is a researcher with over four years of experience in the cybersecurity industry. He attended Kaunas University of Technology and graduated with a Master's degree in Translation and Localization of Technical texts in 2017. His interests in computers and technology led him to become a versatile author in the IT industry. At PCrisk, he's responsible for writing in-depth how-to articles for Microsoft Windows. Contact Rimvydas Iliavicius.

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FIX: Windows Defender Threat Service has stopped. Restart it now [Solved]

On a Windows 10-based computer, the Defender Antivirus Security Center may encounter the error: "Threat Service has stopped. Restart it now." The easy way to fix the problem, is to press the "Restart now" button to start the threat service, but in some cases this doesn't work and you receive a new error message that says "Unexpected error, Sorry, we ran into a problem. Please try again."

This tutorial contains instructions to fix the following problem in Windows 10 Defender Virus & threat protection status: "Threat Service has stopped. Restart it now."

Can’t turn on Windows Defender in Windows 11/10

If you are unable to start Windows Defender, then one of these suggestions is sure to help you:

1. Check if you have another security software installed
2. Check the date or time on your PC
3. Run Windows Update
4. Check Internet Zone settings
5. Check Group Policy setting
6. Check Registry setting
7. Check the status of Service
8. Scan PC with portable antivirus software
9. Check the value of AllowUserUIAccess.

Let us see the suggestions in detail.

1] Check if you have another security software installed

One of the most common behaviors of Windows Defender is that if it detects a third-party antivirus software, then Windows Defender will shut itself off. Windows is designed to detect the presence of security software installed, and we often get to see the notification in the Action Center. One of the common issues we have seen in the past is when thereare multiple security software installed. It often creates a conflict between them and in the end, it creates more trouble than doing any good.Frequent freezing, crashing to applications are some of the commonissues which occur when you install more than one antivirus software.

So to avoid this situation, Windows Defender will turn itself off when it detects another security program. Likewise, if this security application has a Firewall, then Windows Firewall will also stop working. So in caseyou wantWindows Defender to work, then you will have to uninstall your third-party security software and reboot the system.

Often users may be unaware if security software is indeed installed or not because when you buy a new laptop, mostly it comes with a trial version of security software like Norton, McAfee, etc. Then when you install applications like Flash or Java, it might prompt you to uninstall free security scanner when most of them don’t notice. So it’s best to search your PC if you’re not sure if security software is installed or not. Once it’ removed you may need to turn it manually back on.

Type “Windows Defender” in the search box and then press Enter. Click Settings and make sure there is a checkmark on Turn on real-time protection recommend.

On Windows 10, open Windows Security > Virus protection and toggle the Real-Time Protection switch to On position.

2] Check the date or time on your PC

The other issue that could cause Windows Defender not to work properly is the incorrect date or time on your Windows machine. Make sure you have set your Windows clock & date set properly and then try to turn your Windows Defender back on and see if it works fine. It’s strange, but most of the Windows operating system functions work, based on the system date and time. So an incorrect date or time could trigger abnormal behavior in your Windows OS.

3] Run Windows Update

Another important thing that could cause issues is, if you Windows is not up to date, in terms of Windows Update. This could cause issues in Windows Defender or any other Windows core application. When it comes to any security software, it always needs the latest signature updates and other Windows core updates to keep your PC secure. So I would highly recommend running a complete Windows Update, then go into Windows Defender and run an update from there as well. Then see if your Windows Defender is working fine.

4] Check Internet Zone settings

The above-discussed scenarios are the most common ones. Apart from these, there could be some minor issues that could affect the working of Windows Defender. It could be an incorrect Zone setting in Internet Explorer, which you can fix by resetting Internet Explorer to factory settings. Again, if you are using a Proxy server, Windows Defender will not be able to update.

In such cases, you need to make some small changes to your Proxy server.

Press Windows + X and select Command Prompt [Admin]

Type in the following and hit Enter:

NETSH WINHTTP SET PROXY 1.1.1.1:8080 or NETSH WINHTTP SET PROXY MYPROXY.NET:8080

Now reboot the system and see if it works.

5] Check Group Policy setting

Open Group Policy Editor and navigate to the following setting:

Computer Configuration > Administrative Template > Windows Components > Windows Defender Antivirus.

SIn the right pane, double-click on Turn off Windows Defender Antivirus.

Next, select Not Configured, click the Apply and OK button.

6] Check Registry setting

Open Registry Editor and navigate to the following setting:

HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender

Locate DisableAntiSpyware key. If this key is not present, create a new and DWORD [32-bit] Value.

Set its Value data to 0 and exit.

7] Check the status of Service

Run services.msc to open Services Manager. Ensure that the Windows Defender service is started and set to Automatic.

8] Scan PC with portable antivirus software

Finally, it could be a malware itself that’s causing Windows Defender not to work properly. You could download and use Windows Defender Offline Tool or any other standalone antivirus software and run a complete scan.

9] Check value of AllowUserUIAccess

If under Windows Security settings, the option for “Virus & threat protection” has disappeared, then Andrew suggests the following:

Run Registry Editor as Administrator and go to:

Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender\Policy Manager

Set value of AllowUserUIAccess to 1.

These are some common reasons why Windows Defender does not start.

PS: Windows Defender is turned off or not workingoffers some additional troubleshooting suggestions, which may also interest you.

You may also want to check out these posts which help troubleshoot Windows Defender problems:

1. Error 0x800106a, Windows Defender will not turn on
2. Windows Defender Error Code 0x800106ba: Application failed to initialize
3. Windows Defender Error: MSASCui.exe – Unable To Locate Component
4. Error 0x80070422 The Service Couldn’t Be Started in Windows Defender
5. Error 0x80508020, 0x800705b4 for Windows Defender.