PC keeps restarting after pressing shut down button/ holding it down or pressing shutdown in windows

Thanodes

Currently helping a friend diagnose a PC issue as the title says. So far we've done power management, done a cmos reset, tweaked bios options for A/C power loss, turned off some auto wake functions, i've tried turning off hibernation on the cmd, disabled automatic restart, and changed some registry stuff that involves restarts, the last thing I've asked them to do was go on device manager and turn off allow this device to wake on a network adapter. None of these have worked so far and currently I'm at a loss of what to do next. I'm currently thinking it might just be a windows 10 specific issue so we might try upgrading to windows 11 or that it's a hardware issue related to her PSU where it's holding some electricity and not fully discharging after holding down the power button. If anyone has some more suggestions before we buy another power supply to test it would be greatly appreciated!

PowerSpec_MikeW

@Thanodes

See if it's related to a sleep state. Disable fast startup in power options and try it out. Modern PC's don't go into S5 when you shut them down, so that may be where you're running into an issue. If that 'fixes' it there's something waking the PC up with input.

m0sh

Did you check that you didn't accidently put the power button switch connector on the reset switch pins?