I had a similar problem a couple of times, out of nowhere my computer would randomly throw me a blue screen on start up, thing is it never stayed long enuff so i could read wot the prob was! Eventually i found out it had a prob with my video card...not that is was new or anythin - just decided it didnt like it. After a fresh format and reinstall seems to have been ok ... so far!
dunno if thats the same thing but before u do anythin drastic wiv ur hdd try technobeasts advise if it still dusnt help go for a new install then at least you have tried all the options
