really i should have read your topic better, now i'm coming off as sounding like an a$$ who doesn't know what he's talking about. to tell you the truth i would have never replied because i honestly don't know how to fix your problem without testing out your computer myself. i'll try to give you some general troubleshooting advice.
i still think you have a hardware conflict or failure cause by one or a combination of the three things: the motherboard being defective or incompatible, the video card which could be the source of your incompatability, or the most obvious is the CPU is defective.
even though your CPU isn't overheating it can still be defective. you should test those 3 components methodically seeing where the problem is coming from whether its the CPU, mobo, or video.
some boards don't get along well with the newer 8x video cards, you could try testing with an 1x\ 2x\ or 4x video card. maybe by setting the video card to 4x instead of 8x in the BIOS would fix it.
by testing i mean try the parts on another computer to see if they work. with the cpu you need to test for a while to see if it still freezes on another computer.
the first test you should do is resetting the CMOS. it could be as easy as that, but rarely is.
the problem with all of this testing is that i very much doubt you have extra parts to test any of these things. if you can, i would test what parts you are able to and exchange what parts you suspect is bad\ incompatible.
thats about as much as i can think of, sorry about the misunderstanding