Fan kickin on the system reboots

I have a newer compaq EVO D310M. Not even a year old. Fresh XP-pro just re-installed, while working the fan will kick on very loud and fast then if I keep working it will reboot automatically or crash where the power light is on and the screen is black and everything is froze. At this point I have to press the power button to get it back on. I know the it is set to reboot during system failure. What is classified as a system failure and does anyone have ideas on troubleshooting.(processor getting to hot maybe)