Did re-installing fix it?
You may have hard drive problems. During the summer in the heat or if you drive on some rough roads it is pretty tough on the hard drives. This happened to me a few times in the last 3-4 years. My hard drive was junk it got to the point where windows could even complete an install. Replaced it with a new one and whamo it worked. Most hard drive manufacturers have pretty good warranties and are pretty willing to replace it for free if you call and let them know. Seagate replaced my 250gb with a 300gb completely free the only thing they asked is that I send them the bad one. The hard drive had a 5 year warranty by the way.