Can you post your computer specs? (processor, ram, video card, board, psu)
If it just happens when playing game only and just for that specific computer then it could be the video card.
Try downloading
http://www.cpuid.com/hwmonitor.php then run it (no need to install) then play a game then once the game closes, look at the hwmonitor and post here a screenshot of the actual temps or post the cpu temp and video card temp. You can also post information about your PSU, it will definitely help.