Right well the extremely good news is the card is not damaged! The card I believed to be damaged, I just plugged back into the primary port and took the other out started it up and display it totally fine no artifacts or anything, must have just not been seated right?
So to summarize the problem more clearly will explain from scratch what I have done and what the problem is.
I have two XFX 6600GT 128mb which I know for a fact are not damaged, both work fine.
I have a Gigabyte GA-8N SLi mobo, it has a molex port on the mobo to power the SLi, which I have connected up, also there is a chip thing on the board which you need to flip around to enable SLi mode, I also installed the SLi bridge.
In the BIOS SLi is enable and the PCI-E clocks are set to 100MHz.
I have the latest nForce4 drivers and NVIDIA display drivers installed but shortly after SLi mode is enable the screen will occasionaly go blank, then return and after a few times of doing that the image on screen just dies.
I'm using a 350W PSU with a max load of 18A on the 12V rail. I was sure it was due to lack of power, but then I unplugged most of my devices, All that was plugged in was the power for the cards, two disk drives and an optical drive.
I unchecked the 'Enable write checking' box on Display Settings although I am unsure what this even does?
I'm running screen res of 1280x1024x32 @ 75Hz on my 20" Dell Flat Panel.
The problem seems to occur even at lower resses.
What do you guys recommend I try next, install an older driver maybe?