Wow, F8 didn't do anything? You hit it right when you saw a Starting Windows or similar message, or just after the power-on self test finished?

Hopefully some windows experts will post some more stuff, but I'm guessing that you'll wind up reinstalling the os. When I ran windows, I had to do that every few months just to keep things going OK (i always pushed it to the limit and it always broke). Another note, reinstalling on top of the existing os always seemed to lead to problems. A reformat / reinstall seemed the best.

Maybe you could take this opportunity to repartition your disk into a C: (for operating system & programs) and D: (for all your data files). That made it much faster for me when reinstalling.

Again, I hope some windows experts will recognize this problem for you and save you from redoing everything.