I've actually seen this problem quite a bit at work. System Restore never worked when we tried it; it would idle and we'd get no HD activity. May work in this case, so it's worth a shot. Other than that, all I can think of would be using the recovery discs you don't have...
I don't know nearly as much as DEFRON, so he can correct me.
I always roll back two or three System Restores ago, usually works. Rolling back a single restore has never worked for me (which is funny, as you'd expect that one to work, given Windows Update created it...). Of course it doesn't always work, but you only waste a little time trying :shrug: