Pc crashes playing certain games

[athluam]

So for the last year or so since I got my pc when I play BF3 every 5-10 minutes or so the screen goes black and comes up with no signal, and it starts making a weird buzzing noise, as if the game audio is looping for about 3 seconds. It doesn't shut off the pc completely, I have to turn it off and on myself. It happens in other games as well, but no where near as quickly. In Planetside 2 it took nearly an hour I think, and in BC2 about the same, and in Crysis 2 it took about the same as BF3. My gpu drivers are the latest, and I have tried running stress tests (FurMark, 3DMark11, Prime95) on my gpu and psu but they have shown nothing. I took it back to the shop I got it from and they could find nothing wrong. I bought a new DVI cable to see if it was the connection to the monitor, and tried connecting it to my tv as well but it still crashed. I haven't been able to find anybody else with the same issue and nobody seems to have a solution. The game is still running on the pc, and when the screen goes black the lights on the keyboard are still on; I can still turn caps on and off.
The problem has been getting worse over the last few weeks, it shuts off faster and faster.

My pc specs are:
I5 3470
Gigabyte overclocked 7850 2gb
asrock Z77M
8gb ddr3 adata ram
Seagate 500gb 7200rpm HDD
Western Digital 1TB 7200rpm
Antec 650w psu
Viewsonic 22" 75 hz monitor

Thanks in advance, any help would be greatly appreciated

 

[gamep]

your computer graphics card can play the latest games 3d
but your computer cant play the 3d games maybe the settings in high try the medium or low

 

[athluam]

I have tried changing graphics settings, but they don't seem to help much. Although lowering the resolution seemed to slightly improve it, I also tried reseating my graphics card after which I was able to play for almost 2 hours until it crashed, but then later in the day it got worse again.

 

[acid1drinker]

Does your case have sufficient cooling?

 

[athluam]

Yeah, well when I ran FurMark it never went above 71 degrees and in game it doesn't go much higher than 50-60