First, make sure your antivirus is updated, as some viruses can make a computer shut down unexpectedly. Second, take off your computers side panel (while its off
)and clean out all of the dirt from the heatsink. (and all other places while youre at it) If you take the heatsink off, be careful not to crush the core of the processor when you put it back on. Also, on the fan, if you take hold of the blades and pull GENTLY while twisting a little back and forth helps loosen it up. Make sure that all the jumpers/switches are set correctly on the motherboard as an overclocked processor can overheat and become unstablized, resulting in a shutdown.