I have a problem, where when I have two Radeon HD6870 in crossfire, my computer crashes in games. Either just giving me a blue screen of death or the screen just goes black and everything freezes. I have done the following to try and isolate the problem: Run each card on its own, run each PCIe slot on its own, swapped out crossfire links, checked that all the power cables work fine. It seems that the hardware on its own is fine. Switched between 3 different driver version, reinstalled windows. Overheating is not the issue (as the game crashes with in a few seconds), and my power supply is a Corsair TX850W, enough power I should think.
When I untick the 'enable crossfire' button and play games, everything runs fine. Games I have tried playing are Dragon Age: Origins, Supreme Commander Forged Alliance and Medieval 2 Total War.
This is my system:
CPU: i7 2600K
MB: Asus P8P67 Pro
Graphics Cards: 2x Radeon HD6870 (Sapphire)
PSU: Corsair TX850W