Unplug your router for a minute or so. then plug it back in, let it sit for a minute, and try then. Otherwise you will have to call whoever made your router, or who provides your internet access.
I would try this website: While you attempt to perform the network test on the Test Xbox Live Connection screen, IP address status displays "Failed" Under things to try click the setup you have. If you have your xbox set to auto find IP's make sure if you are using a router to enable DHCP.
I'd attempt to reset your cable modem if unplugging your router doesn't work (I'm assuming that is what you're using). There should be a recessed button on the back of it somewhere that you'll have to hold down on for a few seconds with a pen or something with a small point at the end.