So i have had my computer for over a year now with no problems at all, but just recently when ever i have been playing this one game (Grand Theft Auto 4) my computer turns off randomly after about five minutes of gameplay. I've also had GTA 4 for about 4 months with no troubles with it untill now. I downloaded core temp and i ran Catalyst Control Center while playing and I got about a max of 55C for both components so i dont think its a heat problem so i have no clue whats going on.
Intel Core i7 920 @2.66ghz
ATI Radeon 4870 1gb
750w powr supply
6gb of DDR3 RAM@ 1333mhz
I had the same issue with a MMORPG. It started out of nowhere and was pretty random. After some investigation I found that the fan shaft on my video card had gotten gummed up and the fan was only turning a fraction of its original speed. GPU was getting hot under heavy load and shutting the computer down.
You might look at all your fans, heat sinks and surfaces to make sure there is absolutely no dust, pet hair, debris build up that could be causing some heating issues.