I HAVE WINDOWS 7. I HAD THE SAME PROBLEM. IF YOU HAVE ENABLED USER ACCOUNT THIS MAY HAPPEN. PLEASE TRY REMOVING YOUR PASSWORD. AND TRY TO USE A PASSWORD FOR YOUR SYSTEM.
IF YOU ARE USING ASUS MOTHER BOARD DO LIKE THIS
1. WHEN IT IS DISPLAYED 'ASUS MOTHER BOARD.....' HIT DELETE
C-MOS SETTING will APPEAR (A BLUE SCREEN)
2. SELECT BOOT ON THE TOOLBAR USING ARROW KEYS
3. SELECT SECURITY USING ARROW KEYS
4. SELECT 'CHANGE SUPERVISOR PASSWORD' USING ARROW KEYS
5. PRESS ENTER.
6. ENTER YOUR PASSWORD ******
7. PRESS ENTER.
8. CONFIRM YOUR PASSWORD ******
9. PRESS ENTER.
10. PRESS F 10 ON KEY BOARD
11. PRESS Y+ENTER
YOUR COMPUTER AUTOMATICALLY RESTARTS
WHEN IT RESTARTS AND ASKS YOU FOR PASSWORD. ENTER YOUR PASSWORD IN THE BOX THAT APPEARS.
IF IT ASK YOU THE NEED FOR PASSWORD TYPE PRIVACY
CALCULATION: ONLY FOR ASUS