PC shutting down while in game mode

[fozi]

Please help. I've upgraded my PC from 2x2gb ddr 2 ram to 2x4gb ddr3 and my CPU from a dual core to a Am3+ quad core processor. Soon as I start up a game the PC shuts down completely where as before it played games ok. I upgraded as wanted to play the high spec games. Please can you help. The PC runs fine until I start up a game.

 

[HawJin]

list out your specs if you would?