Ive had this happen on my p6t dlx v2 ever since i got it, doesnt matter if i run 21x or 20x multiplier, hit reset on boot and it loads windows fine. Currently at 20x200, ram at 1600mhz, 1.2935 vcore, 1.325 qpi, seems to happen a lot less since i changed from 21x193 though, going by any articles ive read this is a pretty common issue on the p6t dlx v2.