Things you could try. get your voltages set to where you want them for your OC. Then be sure to have A64 tweaker and Clockgen allready downloaded on your rig and ready to run. I would also recomend a program that will put a lil load on the CPU when you fire it up. This will put some heat in the chip and help against cold bug.

So when you boot into windows run (i use Super PI 32meg) program for load. I would recomend doing this at about -24 to -25 celsius for boot up. Then using Clockgen change your values of FSBand Multi to where you want them for OC set in place and then tune your mem timmings with A64 Tweaker. if you prefer to do A64 tweaker first thats fine. Try that to see if that helps.