This is because the user has installed a driver that has not passed verification, causing the system to prevent the user from booting for security reasons. When encountering this problem, please take a look at the following solutions.

1. First, write down the file information displayed on the screen when the computer cannot be turned on, such as C:\windows\system32\drivers\XXX.sys;

2. Restart the computer and quickly press F8 key to the advanced startup menu of Win7 system;

3. Select "Disable driver signature enforcement" in the advanced startup menu and press Enter;

4. Pass the previously recorded Find the file at the file address and delete the sys file.

5. Start the win7 system normally and check whether there is a device with an exclamation mark in the device manager. If so, uninstall the driver and reinstall the correct driver.