check your craphic card's heat with gpu-z
http://www.techpowerup.com/downloads/1207k/GPU-Z.0.2.8.exe my 9600gt is like 43 C in idle and 53-54C in l4d (1280x1024,all settings max.)
check if your gpu cooler/fan is ok and in it's place.
[another possibility]also there is a possbility that there is something wrong with mainboard.
[another possibility]power is not enough.(when you see shaders, or when directx runs GPU needs power.)
If power supply problem is the case, high possbly, your card is dead at the first not-enough-power problem(that smell).
