Probably to late for suggestions, but.
Did you try starting up in safe mode?
Before you go into any extreme measure -- pull your hard drive and copy the "important" files onto another machine. Of, course that does not help with the installed programs. I guess I am assuming you have access to another machine.
Windows does have a fix OS on the disk I have. A couple of times it fixed everything up real nice. One time it made it worse. Had to do a complete re-install.