Instructions
Double-check your network connections. The Xbox 360 must be connected to a router via an Ethernet cable, and that router must be connected to a broadband modem. Unplug the cables from each piece of equipment and plug them in again to confirm they are attached correctly. If you have a wireless router, ensure that your modem and router are connected properly and that you have an Xbox 360 wireless networking adapter connected to your console.
Power-cycle your network equipment. You can do this by turning off your Xbox 360, unplugging your router and unplugging your modem. Wait five minutes; then power them back on in the opposite order (modem first, then router, then Xbox). Once everything comes back online, your connection issues may be resolved.
Restore your Xbox 360 to the factory defaults. You can do this by selecting "My Xbox" on the Xbox 360 dashboard, choosing "System Settings" and clicking "Network Settings." Choose "Additional Settings," then "Restore to Factory defaults." This will not damage your saved game data, but it will erase all network settings and may help to clear a corrupt connection.
Check your Internet connection by browsing to a few websites on your computer. If your computer is unable to connect to the Internet, the problem could be your Internet service provider. Your ISP should be able to help you troubleshoot issues with your Internet connection.
Check the status of Xbox Live by following the "Xbox Live Status" link in the Resources section. While it is rare that Xbox Live is not running correctly, maintenance or other issues may bring the service down and cause you to be unable to connect.