Hmmm...does it just automatically restart? I had a similar sounding problem recently that I fixed by running Windows Memory Diagnostic (http://oca.microsoft.com/en/windiag.asp#top). I had errors up the arse, failing drivers, etc etc. Found that a stick of RAM was just really dusty, pulled it out & blew out all the dust now everything works like a charm.
Just another suggestion for you.
Just another suggestion for you.