Instructions
Factory Reset
Turn on your Xbox. If you do not have a game in the console, you will automatically see the console's main menu. If you do have a game in the console and it begins to play, remove the game CD to return to the console's main menu.
Select "My Xbox."
Choose "System Settings."
Open "Network Settings." Select "Wired Network" from this screen.
Choose "Configure Network" and open the "Additional Settings" screen. Select the "Return to Factory Defaults" option and select "Yes" to confirm your selection. The reset will occur, which will repair all errors with your Ethernet connection that were the result of improper settings with the connection itself. Turn off your Xbox 360 and then turn it back on to complete this factory reset of your Ethernet settings.