A few days ago I was getting the blue-screen-of-death quite regularly.
Upon opening my case the graphics card (Radeon 4890) felt incredibly hot (not sure how hot they're supposed to get). So, I took it out and blasted it with compressed air, got all the dust off it etc etc.
Now, my computer will not boot up at all, and the 4890 had 3 flashing lights on it:
D1601 - Red LED On, shows critical temperature fault
D1602 - Red LED On, shows External power connector A was removed
D1603 - Red LED On, shows External power connector B was removed
The card would start up, pause, lights would come on, then re-start ad infinitum.
It's as if the card wasn't getting any power, however I've checked the power leads many times (I'm no expert however)
I also tried a different card which wasn't powered by PCI-E, and had the same results (card would boot up, pause, then restart...)
I'm now at a loss as to what it could be!
Corsair Hydro H60 High Performance Liquid CPU Cooler
Try removing the card and blowing out any dust they may have gotten into the PCI-E slot itself. Then firmly re-install the video card and connect the external power connections. It is possible you have some crud in place keeping you from connecting the mobo and GPU (video card) properly.
While you are in the case, verify that the 24-pin and 4/8-pin power connections from the PSU and the motherboard are securely fastened as well.