Since i got my new card my PCs been a bit unstaple in the way that i can run my games (FS9, CFS3 + CFS2) fine for about 20 mins then all of a sudden my PC just frezzes and after 7 seconds (on average, yes i did count) then pc would turn it self off

.
The wired thing is that FS9 and CFS3 are played for longer than CFS2??. Also the other games i have Medal of Honour seriers + Counter stirke and Day of Defeat all run fine without any problems ???
Things i have done
Re-installed all games, reinstalled drivers, checked for viruses, defraged and ran a registry cleaner. So to me this only leaves only heating :(
Stiz