A couple months ago I restarted my computer while ChkDsk was running and created this same problem. It would restart as soon as the XP logo popped up.

I tried a few things that didn't help me at all, and because my Finals were approaching I decided I didn't want to spend time messing with it and just left it off. Well, I turned it on about four days later, and it started working again normally. It was extremely bizarre, and I don't know how it fixed itself. But it did.