XFX 6790 Blackout Problem

I have been having ongoing problems with my graphics card. I built the computer about 4 months ago and since then every time I play a game (any, doesn't matter about graphical quality) or even go online, it freezes, blacks out and comes back with a notification saying (Display driver stopped responding and has recovered).

I have been constantly asking forums and even taken the card back and they have sent the original back saying no fault.

There were rumours of something called "timeout delay and recovery" but there's no solution for that. It could also be power but when I go on AMD System Monitor the card doesn't even look strained.

Any help would be appreciated.
Thanks

PC Set-up
Motherboard - Gigabyte Z68A-D3-B3
CPU - Intel Core i5 - 2500k CPU @ 3.30GHz
Graphics Card - XFX HD Radeon 6790
RAM - Corsair CMZ4GX3M1A1600C9 4GB 1600MHz CL9 DDR3 Vengance
PSU - 650W Antec Truepower (also have a 750W but that doesn't solve the problem)
OS - Windows 7 64 Bit

I know you said it's not being stressed when this happens, but what are the temps of the card?

Can you post a screen shot of hardware monitor voltages? something might be off, getting too much or too little voltage causing it to crash when going from idle to load.