Have to agree with Dutcho, most likely sasser, have you got a network cable plugged in?? For network to other comps or router/dsl modem etc? Try unplugging it see what happens, if that stops it from rebooting then its pretty sure bet you've got sasser..
Did you make sure you downloaded the latest version of stinger?There's some pretty good destructions for removing it HERE
Hope this helps...if not some more info would be appreciated