Alienware m17x R3 Gameplay/FPS running really slow

Hello,

I recently bought a alienware m17x R3 about 5 weeks ago and things were going fine up till a week ago. I was playing Modern Warfare 2 at high performance with all setting maxed out and everything was running really smooth and great, the laptop was fine sitting on a table with air ventilation, after about 2 hours through playing the computer shut down (i think it was due to it overheating) for no reason, i didn't bump anything, didn't press the power button just shut down. So the next day I turned it on and went to play the same game, things were really slow, my FPS before it shutting down was about 55-60 and now it is just hitting 20's, as days went by things didn't change so i called customer support. I spoke to this guy and he did a basic clean up and just had a look around if things were out of place, he couldn't find anything so he passed me onto technical support and another bloke spoke to me. He went through a system check, went through my drivers to see if they were ok, my graphics card was out of date so he just updated that and basically did a overall view on the system. After he did this he said things should be fine now, he didn't ask me to see if the game was still lagging or anything just said the system will be fine. So i disconnected and went straight onto the game after rebooting, things were the same...Please help me with this, I don't want to have to go and explain everything to another person in customer support and then repeat the process of just getting a clean up, If maybe a guy can come out and check my graphics card or system because the computer is running really fast but its just games run at low FPS even on the lowest quality.

 thanks, Braxton.