Screen goes black while gaming?

I have a 4 year old MacBook Pro 15-inch, late 2008 model. I got it refurbished but it was barely used when I got it.

Anyway, I love this computer. It's been so good to me, I've only had to replace the battery and the hard drive so far.

It's played all kinds of games from Sims 3 to Portal 2, WoW and Minecraft, with no issues. A couple of weeks ago I noticed

that my laptop was overheating more than normal (Even though I modded the fans with smcFanControl) and when I tried to play Minecraft

the temperature skyrocketed to about 85C. Too hot to touch! It didn't used to get that hot. While I was pondering this, the screen suddenly

went black. The computer was still on, I could hear the fans and the keyboard lights were on, but there was no screen response

and I could hear a loop of the last sound played. What's going on? I used to be able to game for hours with no penalty.

Now I can't run the game for more than 3 minutes before it goes black and I have to force the power off. Same thing

happens with WoW, but not as fast. If I'm lucky I can get in an hour of gameplay. Does anybody know what's wrong?

Things I think may be wrong:

-Heat is messing with the logic board

-Thermal gel is old and useless

-Graphics cards are outdated

Basic specs:

2.4 GHz Intel Core 2 Duo

4 GP 1067 MHz DDR3

NVIDIA GeForce 9600M GT 256 MB

OSX Lion 1.7.3