Instructions
Plug in the HD AV or AV cable you wish to use into the AV port in the back of the Xbox and plug the other side into your television.
Set the switch on the AV port to HDTV if the television supports high-definition resolutions such as 480p, 720p, 1080i or 1080p.
Turn on the Xbox 360 and a controller. Press the middle button (guide button) on the Xbox controller.
Scroll right to Settings and choose "System Settings" > "Console Settings" > "Display."
Choose HDTV settings if you have an HDTV. Select the picture output that your television produces. The screen will go black and then ask whether you want to keep these settings. Choose "Yes" if they are correct. Otherwise, go back and choose again.