Instructions
Start up your Xbox 360.
Press the "Guide" button in the center of your controller. If you are logged into a profile, press the "X" button to sign out.
Press the "Guide" button again. Scroll down to "Recover Gamertag," and press the "A" button.
Press the "A" button again. Select "Yes" to end your current game session, and press the "A" button. Select "Continue," and press "A."
Type in the email address associated with your Xbox Live account using the on-screen keyboard, then press the "Start" button.
Type in the password for your Xbox Live account, and press the "Start" button.
Select your time zone, if prompted, and press the "A" button. Wait for your gamertag to download to the console.