wINDOWS xP

And make a new user Account and see if the new account is complete or blank.

If it's complete that User Accounts that are blank have been corrupted and you'll need to transfer all the data out of then and delete those User Accounts after creating a new account.

You can also scan the system while in the Administrator Account with your AV product just make sure that it's updated first and then some Malware Scanner like Malware Bytes available here

http://www.download.com/Malwarebytes-Anti-Malware/3000-8022_4-10804572.html?tag=mncol&cdlPid=11004434

Col