see if it will boot in another pc, to eliminate your existing hardware or software as the problem, maybe isolate it to just the card.
if it will, then I would start with Windows 8
I have good luck with Win 8 compatibility though, even Windows 7 drivers have worked fine on some stuff
Just on a lark, do you have 2 sticks of RAM? like, can you pull one stick or the other and see if it will boot with just one stick, or in another slot, or something like that?