Instructions
Open your web browser and go to Xbox.com.
Click the green "Sign in" link at the top right corner of the website. This directs you to the Windows Live ID sign-in page.
Enter your Windows Live ID sign-in information into the two text boxes, then click "Sign in." Every Xbox Live user created a Windows Live ID when they signed up for the service. If you do not yet have an ID, enter your email address in the text box below the Xbox Live graphic and click "Join Now" to begin registering. After signing in, you will be directed back to Xbox.com.
Choose the "Support" link, located near the top right corner of the webpage.
Locate the "Console Management" menu on the left-hand side of the resulting webpage. Click "Register a console" beneath "Console Management."
Enter all the information required in the resulting field form. You will be required to fill in personal information, such as address and phone number, as well as console information, such as the serial number.
Select the blue "Submit" button at the bottom of the form to send your registration information.