Instructions
Press the "Guide" button on the Xbox controller and press the "Y" button to sign out if you are signed into an account.
Scroll to the "Home" tab and select "Recover Gamertag."
Enter the Windows Live ID information associated with the Xbox Live account. You will need the email and password for the account. If you don't remember this information, visit the Account Password Recovery page in the Resources section or call the customer support number at 800-469-9269.