Instructions
Go to Microsoft's website (see Resources) and click on the "Support" tab; this can be found in the top left corner.
Click on "Troubleshoot flashing red lights" tab. Select the "Flashing Red Lights Solution" halfway down the page.
Select the number of flashing red lights your Xbox has. If it is a red ring, then select "four."
Check the A/V cable by turning your console and television off. Pull out the A/V cable from the back of your console. Disconnect the A/V connector from your television set.
Reconnect the A/V cable to your Xbox. Plug the other end of the A/V cable back into your television. Boot up the console and the television. This should fix the flashing red ring.