CPU: Amd fx-8150
RAM: 32gb quad channel ddr3
GPUs: Crossfire: ATI Radeon HD 7870 series X2
OS: windows 7 pro 64bit
This has been happening for as long as I can remember. Whenever I play a game (Tested with Counter Strike: Source, Assassins Creed II, and Black Ops II) after 10-20 minutes, the screen loses signal, and I can still hear the game going on for a few seconds after, but then the sound starts to loop, and I can't get rid of it until I hard restart.
I am pretty sure its not the CPU or GPU overheating, as the gpus' temperature stays between 50-70c during gaming, and the cpu is water cooled and stays around 50c.
I had kinda a similar problem and it plaqued me for 2 months. Drove me nuts.
I ended up fixing it by reseating the CPU.
Someone recommended it and I dismissed their suggestion. However when I did it I found the CPU got wedged in the socket. It was very difficult to the the arm bar to release. However once I did and reseated the CPU with new thermal paste everything worked fine where as before it would consisently fail just minutes into games.
Looking back on it I was messing with my PC one day and I think I accidently bumped the Heatsink too hard with my hand. As a result it placed too much pressure on the CPU's memory controller and started causing memory errors when manifested themselves in my games dying at random points.
Not sure if this is your problem but I hope it helps.
2.) You can also run a Dxdiag report.
a. Click on "START"
b. Click "run"
c. Type in "dxdiag" and click "OK"
d. Check through the tabs and perform all tests
e. Click "Save all Information..." and save the text file to a location of your choice
I am not sure how elaborate of a system that you have set up but I know it is a pain to work on. However it is the weekend so if you got time you might want to try it. If nothing else it will give you an opportunity to clean out your case.
Best of luck to you which ever path you choose.
Should you attempt to remove the water block you may want to put it back on with a little less pressure at first just to test.
When I had this problem I was not able to go more than 4 hours with out a crash and that was a rarity. Most often I would not last more than 5 minutes gaming. Youtube would crash streaming video also however that was less common.