Alienware M18rx 2012 constantly Freezing and restarting when playing a game.

Every time I try to play a game (in this example WoW) not 3 mins into it my laptop freezes to a black screen then decides to restart itself. No amount of rolling back drivers or re-installing them seems to work. It boots up fine, I can browse the web or my files, but as soon as I do something graphically intensive it always does this.

I have had a Dell Tech out to my house twice now, and this problem persists. I've had a complete replacement of Graphic Cards, motherboards, pci cables etc but this continues to happen.

Any help or feedback would be appreciated :)