Acer laptop stuck at BIOS screen

Hi to all,
I am having problems with my brand new Acer Aspire ES1-523 [Windows 10].
I wanted to disable EUFI Secure Boot in order to install Windows 7.
From the advanced startup options, I selected to change EUFI Firmware settings, then restarted the system.
The bios started up but I couldn't disable Secure Boot without changing the boot mode from EUFI to Legacy, so I decided to exit without making any changes.
The system started again with the bios.
At that point, I decided to change the boot mode from EUFI to Legacy version, saved the settings and restarted the system. Nothing changed. The bios started again.
Then I restored default settings by pressing F9, saved the settings and restarted the system. Nothing changed. The bios started again.
What's happened?
I hope that someone can help me.
Thanks a lot!
Matt

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