Ok, how about double checking and making sure all the drivers you installed at X64 bit. Just trying to rule all the obvious things out, because alot of times its something obvious. Also, do you have all mobo power connectors connected? I suppose it could be possible your mobo is grounding out... have you moved your tower recently, maybe jostled something? You might try taking the mobo out, putting it on an anti-static bag, and booting up, see if that takes care of the bsod's. Hmmm, other than that im running out of ideas.
EDIT: Also, this instability could be the effect of a failing PSU. I would definatly say you should check your psu's 12v/5v rails and see there are any large fluctuations. If you could, try another psu.