To unlock a computer, use the Ctrl, Alt and Delete keys and the logon details of the user that last logged in before attempting to log in normally. Alternatively, shutdown the locked computer, press Ctrl+Alt+Delete and log in normally. Also, consider changing the password for unlocking the computer.
If the error message shows that the domain/username locked the computer, first press Ctrl+Alt+Delete. Type in the logon details of the user that last logged in, press OK, wait for the Unlock Computer dialog box to disappear, press Ctrl+Alt+Delete again, and then log in as usual.
If the error message does not mention who locked the device, shut down the computer. The Microsoft Windows Resource Kit has a Shutdown Tool, which is used to shut down the computer. A System Shutdown box opens up, but the computer does not start on its own. After the shutdown timer runs out, a Welcome to Windows box opens up. Now, press Ctrl+Alt+Delete before the screen saver activates and log in as usual.
Alternatively, click on Run in the Start icon and type "cmd" to switch to the DOS command screen. Type "net", then a space, "user," then a space, and the username and press Enter. Now, enter a new password and retype to confirm it. Type "Exit" to switch back to the login screen. Unlock the computer using the new password.