I saw this problem once a few months ago. I did some looking around for a solution, and found the same answer everywhere I looked. You will need to create a new account, and then login under the new account. Go to the Documents and Settings folder and copy the folders from your old account over to the new one. This will at least setup your desktop, favorites, cookies, and my documents like they were in the corrupt account. I never found out what causes an account to be corrupted, but I do know that it isn't a sign that you need to reformat. Hopefully you haven't done that yet, because setting up a new account is quicker and simpler.