please help, my computer display is shutting down more and more

[ghastaphish]

Hello all. Here's my build:

Intel Pentium G860
Powercolor Radeon 7850 HD
Coolermaster Extreme Power Plus 500W psu
8GB RAM
Seagate 500GB HDD
Asrock H77m micro ATX mb

So, originally, this used to be an issue that only happened when I would play video games. I'd be in-game for anywhere between several minutes to a few hours, and the screen would go black, in which case I had to restart the computer. Sometimes the black screen would also be accompanied by a weird screech coming from the speakers on my HDTV monitor. Now the problem seems to have escalated to the point where even if I'm just using a web browser, it will go black, forcing me to restart. What could this possibly be from? My GPU and CPU temps are both fine. I have all the latest drivers. Could it be a compatibility issue with my HDTV monitor and the video card? Maybe a PSU issue? I know the one I have is pretty terrible, especially for my video card. Please, any help would be appreciated, this has been happening for a while now and I really want to figure it out.

 

[ghastaphish]

Update: I purchased a much better PSU, and the problem persists. Any other ideas?

 

[ghastaphish]

Ran Memtest for 9 hours, no errors. Now I dont have any sound coming out of my monitor...