Hardware/software problem?

I'm kind'a new here. someone from yahoo answers recommended this site. I hope you guys can help me.. here it goes: my uncle's computer usually restarts by its own will and when it turns back on the monitor will show as if there are no "chipset drivers" has been installed yet and no matter how I adjust its settings it won't work. At 1st I thought it was just a virus thing so I tried to reformat it and installed everything that needs to be installed. It was on for about 2 hours and then it restarted itself again going back to the same problem. i need you guys to help me. The computer by the way is pretty new. He bought it a few months ago. Is it a software problem? because if it is... it should have been resolved by reformatting it.. if it is a hardware problem.. what could be it's problem? what do I need to do. Please help me with this.. i would really appreciate intelligent answers. thank you..