No make or model so let's call it the usual clone job.
Did you try it with the cover off and complete the cleaning noted at http://reviews.cnet.com/4520-11319_7-6240575-1.html ???
I run a desktop with windows vista, SP2. Lately it has been having crash issues. How quickly it happens varies, sometimes it goes for a few hours, most of the time it lasts 5-10 minutes, sometimes it won't even get to the log in screen. When it crashes it seems as though all output from the computer simply ceases. The monitor resets to its 'looking for input' mode, sound cuts out, keyboard's display cuts out suggesting it loses its signal as well. I thought at first it might be an overheating issue so I added some extra cooling in the form of fans, but that doesn't seem to have an effect. I can provide hardware specs if needed. The video card is a nvidia 480 gtx, which tends to run hot which is why I thought it may be a heat problem. Other than that I would have to go back and look at what I have in it for hardware.