Hi ,
Try the given steps and let know if that helps!
1. Restart the computer in selective mode,follow the steps mentioned in given link:- http://windows.microsoft.com/en-us/windows/run-selective-startup-system-configuration#1TC= windows-7
2. If still issue persists, unhidden the Administrator user account, steps mentioned in following link:- HOW TO: Enable the build-in Administrator account in Windows Vista
Sarika