Game issue in general

This is a major problem for me.

Whenever I start up a game the program will run just fine for the first minute or so. But after that, the screen will explode into a multitude of colors. The computer at this point will no longer respond to any outside stimulus.

After a few more seconds my monitor reports that it's no longer connected to the computer, it will then go into power saving mode.

in about 30 seconds the computer will automatically restart.

This problem occurs whenever I open any type of game. It very rarely happens if I do work or surf the net.

Any suggestions?

-Spectre