Restart the computer then follow next steps:
1. Press on the F8 key while you start Windows 7 until your PC displays the boot menu.
2. Select Safe Mode option and press the Enter key
3. Then a login box appears, click on Administrator in the username box and leave the password field as blank, click on OK to login.
4. Now you can open Control Panel, then in User Accounts you can reset any user password easily.