computer freezes while playing bf3

My issue is simular to alot of the other BF3 issues I have read on here, I can get the game started and be playing but when it comes to a heavy graphics spike in the game or most of the time at the end of the rounds when its tell you if your team won or lost my computer freezes, the video shuts compleatly down (including the monitors), there is a god aful sound through the sound card then nota...no blue screen....just nothing...the lights on my caes are still on but ctrl/alt/delete dosen't work and I have to manualy shut the system down and restart...sometimes I can play the game for hours on end with no issues but latley this problem happens when I first start playing a map but majority of the time its during game play or at the end screen....I have tried deleating and re-installing all of my ATI drivers, I have tried rolling back to previous versions and no help, I'm almost to the point of compleating whiping my HDD's and doing a fresh install of Win 7 64 and going from there....any info or advice would be greatly appreciated....my system specs are as follows:


Windows 7 64bit
Foxconn A7DA-S motherboard
AMD Athlon 64 X2 6000+ Cpu (3.1 ghz O.C. to 3.4)
1 Sapphire HD4870 Toxic series Vid Card (1gb mem)
4gb (2gb sticks) of G-Skil 1066 DDR2 Memory
2 360gb HDD's (7200 rpm)
6 cooling fans (including the CPU cooler that would be 3 120mm, 2 220mm and 1 200mm)
Asus 120mm Artic Freezer CPU cooler
Sunbeam 680 watt PSU
1 Sietek Cyborg command unit and gamming mouse

Could this be a PSU problem, a different hardware problem or could this just be another case of a game creater releasing the game way to soon with too many compatibility issues.....my problem ONLY happens with BF3, all my other games run and play fine at all high settings....