The only thing i can think of that would cause an auto restart like that would be a flat battery (all comps have a small button battery to hold the time and date) other that i can't help
Yeah, maybe you should try clearing the CMOS. Just take out the battery on your motherboard for about 5 mins. Put it back in and let us know if it worked. I hope it helps!
Some PCs are automatically set to power on when they receive mains power. It could be a problem with the motherboard (which might be solved by clearing the CMOS as suggested) or it could be a problem with the power supply, falsely recognising a new power signal.
What make is the PC?
