My PC has been showing unusual signs of life lately. When I shut it off(not restart or stand by, but real OFF) it runs through the typical procedure and shuts down. But after about a minute, the motherboard gives its traditional single beep and the whole thing comes back on. For that minute it seems to be truly off, but as I said it then comes alive.
If I turn the power off at the power supply it will stay off even once I have set the switch back to On. Any ideas on why this behavior would suddenly emerge?
This is unusual, but my first guess is that the BIOS has become corrupted or you have done a some changes in it and accidently set it to come back on after any power off situation. Alternatively, you might have picked up a virus where someone else is controlling the machine and the virus has activated an automatic restart.
Powering down by use of the power supply switch over rides any changes because the virus or other change cannot exert any control when there is no power coming in.
A third possibility is that the power button and/or reset switch is malfunctioning. This might make more sense, considering that you have trouble restarting the computer after you have manually shut down the psu. Beyond that, your computer may be possessed.