7800GTO SLI problem

Hi everyone...

I've bought a couple of 7800GTO's the other day. Replaced my 7800GT's with them. Now my problem is that although my desktop is fine, when I start games up, BF2, BF2142, Supreme Commander. I'm getting green artifacts in places on the screen. Now I know that this is supposed to show that I've got bad memory on one of the cards. Problem is that when I try the cards out singley I don't get the artifacts! Anyone had this problem before?
So far I've tried downgrading the drivers to last two previous versions TNA! Also tried using coolbits to underclock the cards. I've also tried reflashing the cards up to GTX. Nothing seems to make any difference when they're SLI'ed. I want to return the cards, but all I've been told is to run serious stress testing on the cards individually.

My system specs are:
CPU - AMD 5200+
MOBO - Gigabyte M590SLI-S5
MEM - 2 x 1GB Corsair Dominator PC2-6400
PSU - Tagan TG580

wait are they brand new?? Return them ASAP if so. Get a 8800GTS or GTX. It sounds to me like they are underpowered.

That's the problem... The place where I bought them from won't give me an RMA, and won't receive any goods back unless they are marked with an RMA number... So in effect, I don't fancy have these two cards buffeting around in the post back and forth...

I guess the only way out is to buy a new PSU to see it they are actually underpowered at the moment... I can't beleive that the 7900GTO's use that much more power than my older 7800GT's...

7900GTO's or 7800GTO's?

2 7900GTO's will take about 2X the power of 7800GT's

They are 7900GTO's...

I've ran several power consumption tests online and they've all com back with virtually the same results, my PSU is more than capable of running the system at 100% utilization with the 7900's installed...