I've had Dual 7870s for awhile now probably 5-6 months. Never had a problem really until just recently I get BSOD whenever I try to play a game in fullscreen ( because crossfire only works in fullscreen ). If I disable crossfire it works fine. I've confirmed both cards work 100% by swapping them out and using them individually. My power supply its a corsair HX750 and it's not very old. I've never overclocked the PC because well... there no need. The PSU more then suffices the Wattage needs and I've measured all the voltages and they are either SPOT on or off by such a minimal amount that it doesn't matter. This BSOD started when I swapped one of my monitors for a 144hz BenQ one. before I was doing a dual monitor setup with a 1080p 60hz monitor and a 1600x900 60hz monitor. After I swapped I still ran games in crossfire fine but a few days later and causes unknown I Blue screen every single time. I've tried going back to my old monitor setup, disabling 1 monitor, running the 144hz monitor at 60 hz and even tried having one plugged in HDMI and one in DVI and tried everything I can think of. My hardware seems fine and this leads me to assuming it's software related. So I uninstalled all Drivers cleanly and completely and reinstalled the stable 14.4 catalyst instead of the Beta drivers I usually use and I get the same thing. I've run out of ideas at this point and since I have no proof that any of my hardware is failing ( once again I've tested both GPUs and the PSU ) I have to assume something is up with my software.
So I'm calling on the awesome community of brainiacs here who might have had similar situations for help. The only thing I did is disable the power saving thing on the 2nd card through the registry because I was having issues with the 2nd card not even working in some games ( cough farcry 3 ). But this was before I even had the new monitor and it was working perfectly fine for weeks after I did that.
Also I can't say what errors I'm getting because the Blue screen is completely artifacted ( not a word ) and unreadable which is SUPER annoying.