GPU Causing Black Screen/Crash?

Hey, i built my first computer and at first it was running slow so i re formatted the HD and re installed Windows, well, that did the trick! Now i have another problem, whenever i try to play games, any game, any stress test, benchmark, anything what puts a little stress on the Sapphire HD 7850 card, it crashes the computer (black screen, looping the last sound on the game) and i have to power off the computer and turn it back on.
this is the specs:

Windows 7 64bit
Gigabyte H81M-S2H Motherboard
I5 4570 Processor
Evga 600b 600 watt PSU
Coolmaster 103 cpu cooler
Sapphire HD 7850 2gb Dual X GPU
Fury X 8GB Ram Stick

These are the steps i have done after searching for 4 nights online to try and solve this issue..
Memtest - No errors
Re installed/Updated Drivers - No change
Disabled igfxservice from services as i got an error in event viewer at one point before a crash (cant remember the actual name) - no change
Disabled Onboard Graphics from bios - no change
Disabled Overdrive from Catilyst Control Centre - no change
Disabled Ulps- no change
Disabled onboard Audio Driver - no change
Updated motherboard Bios - no change
tried the second power pin to the gpu - no change
Enabled Legacy PCI-E in bios - no change
Underclocking the GPU with MSI Afterburn - no change

All the temps are fine, around 52c when in game or benchmark and it doesn't happen when i'm not gaming.
I think i know what some people are going to say, but i really hope there's another solution as i can't afford to buy another one yet. I'm lost on what else to try now, i'd appreciate any help on this!

Test in another system if you can... otherwise, it may be the card.

I'm unable to check in another computer, all my friends use laptops.

1. are you useing a Expansion sound card such as a xfi or xonar?
2. what cable type are you using to your monitor, and what Resolution - FPS - Mhz are you playing at.