I had a problem like that recently when i upgraded (not as impressive as urs mind
)
I had a dual-display with a GeForce and an old PCI Savage, when i upgraded i replaced the GeForce with a Radeon aswell as a few other things, and it started freezing randomly.. no errors just totally frozen. Once i removed the second gfx card it worked fine. I can only think it has something to do with ur gfx + mobo combination or something as thats the only time Ive seen that kinda prob.
Hope this helps m8, an hope u get it working soon (nice spec btw
)