Desktop PC boots on a key press, even after mains 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.

It's PS/2 keyboard.

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?

Sounds like there's still residual power being stored in the component(s). Bit of a weird one, though.

Are you saying the PC powers up even with the mains plug unplugged?

No, I said that after replacing the mains plug the PC booted up on any key depression.

A totally weird one. It'll be next month before I can get over to do any more checks, I know the guys in the PC shop that supplied it, I'll call in and ask if they've any thoughts.

Edited by cheshire_man (Sun 16-Dec-18 07:00:35)

Log Windows shutdown states. Sounds like it's hibernating, despite being shutdown. See S4.

https://docs.microsoft.com/en-us/windows/desktop/pow...

Maybe also check the Sx states in the BIOS.

Interesting, well worth investigating.

Inevitable question. On my PC I can't see where I can either cause the shutdown states to be logged, or where they are logged. I'd have presumed they'd be in the Windows/System log file.

Win Key + R

Type: "Eventvwr.exe"

On the menu on the top left, navigate to Windows Logs / System. Right click it and select "Filter Current Log". In the pop-up, enable the "Information" tick box only. Then within the list of log entries, scroll to one or more periods of shutdown.

There will be a collection of lines for a given shutdown, as each process and service is terminated, but the first one of that batch should be the initiated shutdown by the user, perhaps labelled as source "USER32" or similar.

Here are my most recent (personal info in [Square Brackets] ):

The process Explorer.EXE has initiated the power off of computer [Computer Name] on behalf of user [Computer Name\Username] for the following reason: Other (Unplanned)
Reason Code: 0x0
Shutdown Type: power off

This then initiates the shutdown, with the next log being:

The process C:\Windows\system32\winlogon.exe ([Computer Name]) has initiated the power off of computer [Computer Name] on behalf of user [Computer Name\Username] for the following reason: No title for this reason could be found
Reason Code: 0x500ff
Shutdown Type: power off

The logs that follow are a mix of services being stopped. The last two are:

The kernel power manager has initiated a shutdown transition.

and

The operating system is shutting down at system time [etc].

What you need to look for is if the computer was put into Sleep, Hibernate or Shutdown, and perhaps look at the first couple of logs as it starts up.

For what it's worth, my first two shutdown logs are coded as 1074, with the last two being 109 and 13, and the startup code is 12. Hoping you see something different to help with the investigation.

Bell, book and candle required maybe ?

A bit late to the party, but yeah, it's not shutting down 100%. Almost completely convinced that it's in hibernation.

If you turn off hibernation and standby modes completely I bet this problem will go away. Then you can start to re-enable things one by one until you find the option that makes it act wonky. Good luck. These type of diagnostics are nightmares...

This is a great method!