Reset PC stuck on infinite reboot, can't enable safe mode

Hi!

I have recently been trying to reset my son's PC to factory settings so my other son can have it.

I logged into Windows (Windows 10) did a system reset then waited. It now appears to be in an infinite reboot cycle. I can't find a way to boot into safe mode. I've read that I need to press the shift button when clicking 'restart' on the login screen but the PC doesn't let me get as far as the login screen.

I would really appreciate some advice on how to enable safe mode, please.

Thank you.