To check if you have CPU over heating, which probably is, install a software that checks your CPU temperature. One of the tools I use is Everest.

http://www.softpedia.com/progDownload/Everest-Home-Edition-Download-16369.html

Download and unzip the file, and run everest.exe. This software gathers your system information. Go to Computer -> Sensor. Check the Temperatures.

http://www.pantherproducts.co.uk/Articles/CPU/CPU%20Temperatures.shtml

Check if you have temperature higher than the maximum temperature the CPU can withstand. If so, your computer is over heating. Check if the fan (on top of CPU) is working well, and heat sink is attached to the CPU.

Also check the motherboard tempearatures.

Does the computer have proper heat outlet? Keep the heat outlet away from walls.