Reset the Administrator Password
Q: We inherited a PC. We can reset the PC password, no problem. But how do we reset the password to access Safe Mode, etc? - Ted Searle.
A: If I understand correctly, you can log on as a user but you do not have the Administrator password. As long as you can log on with an account that has Administrator privilege you should be OK. In XP or Vista, click Start, click Run, enter "control userpasswords2" with no quotes, and don't forget the 2 at the end.
In the dialog that appears is a panel titled "Password for Administrator." Click the Reset Password button in this panel, and assign a new password that you'll remember but that a malefactor or a virus like Conficker won't guess.
If that button is disabled, check the box at the top that says, "Users must enter a user name and password to use this computer." That will enable the button. After changing the Administrator password, close the main User Accounts dialog by clicking Cancel rather than OK. That way, your change to the "Users must enter..." checkbox won't actually change anything. - Neil J. Rubenking.