Computer shuts down during games

While playing games the computer shuts down. We have had it in to be checked out. Got it back after we where told the problem is fixed, and it still shuts down while playing games. It runs fine just as long as you dont play games. Any ideas on what is causing this. We have changed out the power supply, swapped out the video card, added ram and it still shuts down. TIA

Can you give some more details on what happens when it shuts down? Does it freeze, crash with a blue screen, power off? Also please Go to My Computer > Control Panel > System In the dialog box that comes up, write down everything that shows under the 'System' and 'Computer' heading (we don't need any of the 'Registered To' information). Post that information as a reply to this thread.