black screen and sound loops while playing games

[gelson]

Hello,
ok so my computer was fine and this didnt happen before i bought my new graphics card, nothing ever crashed when i had my old radeon 5670 in, but because of newer releases, i decided to buy a sapphire 7870 2gb overclocked edition so i could play games such as battlefield 3, skyrim etc. But ever since i installed my new graphics card, when i play games it crashes to a point where i have to manually shut down my pc and reboot it, sometimes i can last for hours playing games without crashes but sometimes it can take just minutes. the games that crash that i have tested are: battlefield 3, skyrim, fallout NV, league of legends, dead island, arma 2 and saints row the third. I can run these games on the best settings with no lag also. Eventually i got sick of it crashing so i sent it into a store where i bought the graphics card and they spent a week testing my games, they noticed that i didnt open the flap that let hot air out and they also noticed that i didnt have all of the pins connected to the motherboard, they fixed this straight away but still took my pc in to have a futher look, they tested the graphics card on a set up motherboard and ran stress tests and memory tests and they all passed, they also tried it on my pc and it passed. They made sure all my drivers and bios was updated aswell. The people at the store told me that i should buy a new case so prevent overheating if the crashing is still a problem and thats what i did because when i got my pc back, it crashed again during a game of LoL. My new case has about 3 fans and plenty of space but it still crashes during games, so i sent my pc back into the store and they played LoL and they experienced the crashing that i had been getting, so they unistalled my hard drive and installed i new one to test to see if its that, and they told me that LoL played for over 4 hours without crashing so theyve found the problem, so i got the pc home again and i formatted my hard drive and reinstalled windows 7, i played LoL for about 20 mins and no crashes, i played abit of arma 2 and then about 2 hours of Fallout NV and still no crashes. But then i tried to play Arma 2's campaign and 30 mins in, it crashed. I tested LoL and i played a 43 min game and it didnt crash but after that game it crashed another 3 times. I have run out of idea's on why its crashing, every driver is updated, i have a big enought power supply to run it (650W) my specs are:

i5-2300 2.80GHz
11gb ram
650W power supply
Sapphire HD 2GB 7870 overclocked edition
windows 7

my card works performance wise, all drivers are updated, ive tried uninstalling CCC and ive tried installing the beta update but still no luck, at the minute trying to fix this has costed my over £100 and i really dont want to spend anymore on it, can someone tell me whats causing all these problems and how i fix them? or if its just my graphics card having a fault? someone please help!!

[must_kill_ati]

I'd be looking at your temps. Are you monitoring your temperatures with any software?

[rievhardt]

it's the card itself... it a known issue now.

anyways try this...

update your mobo BIOS to latest (be sure to know how to flash BIOS)
use 12.7 beta from AMD (install all but do not install the accelerated video transcoding) 12.3-12.8 doesn't work only 12.7, I noticed that 12.7 has an option not to install the accelerated video transcoding...
update all your drivers including sound drivers
turn hardware acceleration off from all your browsers

it's already a month since I haven't encountered the black screen issue.
it's the first time I had a black screen free experience with my pc, it normally occurs within 1-2weeks of gaming...
I hope this is a 100% solution...