This is driving me crazy. I have two 6950s with XSPC waterblocks. I was having issues getting crossfire to run so I decided to pull each card and test them one at a time with the waterblocks installed. I came to the conclusion that one card was not working correctly since it just gives me a black screen in furmark and the system locks up. So to confirm that the card was in fact dead I re-installed the stock cooler and low and behold the card worked perfectly fine. So I figured that it was just a bad mount of the waterblock causing the issue so I reinstalled the block and I am still having the same issue. Anybody have any tips for me since I am going nuts trying to figure out why this is happening. Now just to confirm, I have tested both cards in both PCI-E slots both with and without waterblocks on multiple different driver sets. One card is perfectly fine both with the unlocked shaders and locked shader bios with either the water block or reference cooler in both slots. The other card black screens in fur mark, locks up in catalyst control center, and black screens in every game in both slots with the water block on using either the default bios or unlocked shader bios. But when I slap the reference cooler back on it works fine in both slots with both bios. Probably a long shot but I am hoping someone can give me some advice.