Things You'll Need
Instructions
Look to see whether you have a Comcast router or a modem. Comcast provides or installs a router and/or modem for the Internet depending on your service plan. A router can handle multiple network connections, such as your Xbox 360 and computer. A modem can only handle one network connection. This means that you must unplug your computer from the modem if you want to connect to Xbox Live. If you have router, then connect through the router. If you don't, then you must use a modem.
Connect your console to the Comcast modem or router. Modem: Turn off your console and unplug your modem from the wall outlet to power it down. Connect the two devices via Ethernet cable by plugging one of the cable into the port on the back right of the Xbox console and plugging the other end into the output port on the modem. Turn on your Comcast modem before turning on the console, then wait for the modem to connect to the Internet. Router: Connect the Xbox 360 and router together via Ethernet cable by plugging one end of the cable into the port on the back right of the console and the other end into an available port on the router (there should be several ports open on the router to choose from; any one of them will do).
Turn on the console and test the Xbox Live connection by pressing the "Guide" button on the Xbox controller, going to "Settings," then choosing "System Settings." Select "Network Settings" from the next menu, then choose "Test Xbox Live Connection." Your console will connect to Xbox Live.