Instructions
Disconnect the devices connected to your network. These devices could be other game consoles like Nintendo Wii or PlayStation 3. Computers connected to the network can also complicate the NAT on the system. Turn off the devices or turn off the networking to simplify the NAT.
Unplug other devices connected to the cable modem or wireless router. If you are using a home server or a network backup device, remove the Ethernet cables from your router.
Connect an Ethernet cable to the Ethernet port on the back of the 360 and then plug the other end directly into your cable modem.
Turn on your 360 and click n the "My Xbox" icon. Click on the "System Settings" icon and then click "Network Settings."
Click on the "Wired Network icon and click the "Test Xbox Live Connection" icon. Wait for the Xbox to connect to the network without a strict NAT.