To enter the safe mode when your PC is booting, press F8 at the moment the computer vendor picture disappears, before Windows logo is displayed. If you can see the Windows logo then you failed to press the button in time. In this case, you need to wait for the Windows system login window to appear, shut down and reboot your PC.
If you managed to press F8 key in time, you will see the Windows boot menu on the screen.
Use arrow keys to select a boot mode you need, and press Enter.