Did you build this yourself? What motherboard do you have? What operating system XP?
You should turn off "Automatically restarts".
Right-click My Computer->Properties->Advanced tab->Startup and Recovery Settings-> System Failure
That will hopefully stop it from rebooting itself. From there you may be able to glean more information about the issue. It should at least tell you which program died on you.
It sounds like a hardware conflict or a driver issue.