Virus?

[Bluesummers]

Is there any kind of virus that will restart you're computer, after you shut it down? Because I tried three times last night to shut off my computer and made sure that I clicked Turn Off... and then a few seconds later it turned back on...

[Doomulation]

No, there are no such things... when your computer is off, then it's off.
Creepy... pull the plug and it can't ghost on you ;)

[Miretank]

Defo. Exorcise your computer plz. :P

[Bluesummers]

okay just makin' sure I didn't screw up my computer, it was pretty freaky.

[WhiteX]

Check your PSU and your CMOS power settings.

[Bluesummers]

the wha?

[WhiteX]

Power Supply Unit, if a certain component, the one who makes the comp leave standby mode, is faulty, the computer can power on by itself if plugged to a power source.
You CMOS (BIOS) power settings can have your PC to autostart on the face of Lan or modem incoming traffic, so it is nice to disable those features if they are the causes to your ghost PC.
If you do not understand jack of what i just said, take your pc to a qualified technician or repair shop.