Instructions
Check the AV Cable
Go to the back of your Xbox 360 console and check the AV cable to make sure it is inserted into the console correctly.
Disconnect your AV cable from the back of the console and then put it back in.
Unplug the AV cable from the back of the console and wipe the metal pins on the back of the AV plug with a clean rag.
Try using a different AV cable to test your system.
Restart Your Console
Press the "Power" button on the front of the Xbox 360 until the unit has powered down.
Disconnect the AV cable from the back of the console.
Disconnect the power supply from the wall socket.
Allow the unit and the power supply to cool for a couple of hours.
Reconnect the AV cable and the power supply to the back of the console. Turn your Xbox 360 back on.