Yes that is the only logical explanation. That or Nazis.

And that's the reason why I disconnect my PC from the power grid every time I go to sleep. If it wants to become sentient, it can produce it's own electricity.

I think that Windows Update is set to wake up a PC on 3 am as default setting.

Skynet... had awoken.

Easy way to stop it would be power it on then throw holy water all over it to remove any nasty spirits that may be haunting it!!! I can guarantee this will work and it will stop your PC from booting permanently! (Dont try this at home kids, I have been shocked by a faulty PSU and it knocked me across the room when it arced)

By any chance have you bought Ghost Master from GOG, some of the ghosts on that can attach themselves to electrical items and make weird things happen. Maybe one got free from the game and is doing something to your PC.

Well if I said in the morning I meant in... hmmm.... OK, truth is it was 10:40. It was still on in 3 a.m.
I observed it after waking up (with sharpened stick ready) and only thing that was updated was Avast but Avast updates itself almost daily.

Unfortunately I don't own Ghost Master but it would explain it.

Don't know about you, but I have this power-saving "do stuff half-awake without remembering any of it" feature. I've turned on the computer quite a few times like that.

+1. I use this feature on my customer's machines, so they can turn on the PC with the main power switch instead of turning on the PC separately after the main switch is on. Saves a little time and keeps them from opening the PC cabinet door and letting in dust and dirt.

Edit: it's called something like "Power on after AC loss", and then you choose yes or no.

USB requires active polling by the CPU, while PS/2 sends an interrupt, which is why n-key rollover keyboards are all PS/2 (and most of the time come with a USB adapter, but using that only allows 6-key rollover, not the full keyboard). This is why a PS/2 keyboard can trigger booting, while a USB keyboard can't.

On a side note, my computer frequently wakes up if I set it to hibernate but stays shut off if I chose to shut down completely.

Step 1: Get a cross
Step 2: Get a bible
Step 3: ????
Step 4: PROFIT

Well I was certainly still in bed when it happened so no, it can't be the case. :-)

This sounds plausible. I'll check later if I have this checked.

Also, it certainly wasn't sleeping, it was shut down as much as it could be. Only hammer could shut it more. :-)

Oh, so it wasn't plugged in. Well that certainly makes it far more creepy.

We don't even have electricity in here!

That's what the sledgehammer is for.