Microsoft created both Windows Vista and Windows 7 so that the default administrator account is not accessible and enabled for use. When you have difficulty installing software or troubleshooting a problem, you may need access to the administrator account in Windows Vista or Windows 7 to solve the issue. Use the utmost care when running your Microsoft operating system under the administrator account because security controls do not function in this account.
Click the "Start" menu, select "All Programs" and open the "Accessories" folder. Right-click "Command Prompt" and select "Run as Administrator" from the drop-down menu. Click "Continue."
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Enter "net user administrator /active:yes" in the command box and press "Enter."
Log out of your account on the computer.
Look for the new account on the log-in page. You should see the new "Administrator" account along with any other user accounts.
Log in to the administrator account -- no password is necessary to log in. Set a password if you desire.
Disable the administrator account after logging in to your regular user account. Repeat the same steps you performed to enable the account. Enter a “no” at the end of the command prompt instead of a “yes” and log out of your account. You should no longer see the administrator account.