Desktop PC powers up on any key press - even after power unplugged

I was visiting an elderly friend's yesterday evening and while there was doing some health checks on his PC. I found a most unusual issue.

Having powered down the PC, I happened to press a keyboard key and suddenly realised the PC was booting up.

After checking I found that even after closing down, removing the mains plug, then replacing the mains plug, any key depression is starting the boot process.

I checked the BIOS and the "start on key press" feature is disabled. To double check I enabled it, then disabled it. No difference.

The PC is a dealer built system, some 4-5 years old and is otherwise working fine. The motherboard is a Gigabyte GA-H61MA-12V.

I've not seen this on any PC in the past. Any thoughts?

Check the BIOS again, do you see a Wake on USB or USB charging enabled or similar? Disable these. Also there is a setting when you have a power failure. Change it to Off.

It's a PS/2 keyboard.

Sorry, when originally writing the post I'd said it was a PS/2 keyboard, but in editing before posting I managed to delete that piece of information

Check the last option. On Power Failure change from On or Last State to Off. This could work. Also see for Wake on PS/2 or similar and set it to disabled

Thanks for the thoughts.

Looking at the motherboard manual - I have an e-copy on my PC - I can find:

AC Back
>Memory - last known state
>Always On - turns on upon return of power
>Always off - stays off upon return of power (default)

The second of these isn't applicable as, after closing the system and it powering itself off (not power failure), I then pulling the plug, after 30 seconds I replaced the plug. after waiting for 60 seconds nothing had happened. It was only when I pressed a random key that the PC immediately started to boot. I think the same logic can be applied to the first of these three options as well. However I haven't specifically checked this option so can't be absolutely sure of its setting. I do know that there is no way the friend would have been into the BIOS and changed anything.

The following section also has 3 options

Power on by keyboard
>Disabled (default)
>Any key - Press any key to turn on the system
>Keyboard 98 - Press POWER button on the Windows 98 keyboard to turn on the system

This option is set to Disabled.

Can't find any other relevant BIOS settings.

Just looked at the manual for my (different) Gigabyte motherboard. It has similar settings though worded differently. Haven't specifically checked them but will do when I can next reboot, but mine certainly doesn't wake on key press.

It'll probably be next month (next year!) before I can get over to check other settings.

If It were me, I would take out the CMOS battery and leave it out for approx. 10 mins. Then replace it. This should reset the BIOS to default. The default power-on options are set to 'OFF'. There is also usually a jumper on the motherboard that will accomplish the same thing as removing the battery.

Of course you must then set the date/time and the storage controller (AHCI/IDE mode) otherwise Windows will not start and you could see a blue screen (BSOD). In fact you must do anything that was different to the default settings.