Instructions
Restoring Your Xbox 360 Settings Through the Dashboard
Navigate to the "My Xbox" row of the console dashboard.
Move right and select "System Settings." Ensure that family settings are not enabled, as they will prevent the next step from succeeding.
Select "Initial Setup." The console will now guide you through the configuration process you completed upon first turning on the console.
Resetting Xbox 360 Display Settings Using the Power-Up Method
Turn off the Xbox 360 console, removing any disc left inside of it before powering it down.
Press the Xbox guide button on the controller to restart the console.
Press and hold the right trigger and "Y" button at the same time as the console powers up. Once the Xbox logo appears, the console will restart itself.
Release the right trigger and "Y" button. The console will restart with all display settings reset.