Sounds like the router in my opinion, if all other internet access able stuff work like a tablet, laptop, etc then its your Xbox IP witch you got to call the company for that but I hope I helped.

either try getting a new router or calling up customer support.
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Carnage your Wifi connect setting's on your router.

Go to: 192.168.1.1 or your Default Gateway

Then to the wireless or wifi tab

Then change yoor connection from Static IP to Dynamic. Then your issue should be resolved.

Based on my research it sounds as if it's a dhcp issue, Dynamic Host Configuration Protocol; The Dynamic Host Configuration Protocol (DHCP) is a network protocol that is used to configure network devices so that they can communicate on an IP network. A DHCP client uses the DHCP protocol to acquire configuration information, such as an IP address, a default route and one or more DNS server addresses from a DHCP server. [ Register or Signin to view external links. ]

If your dhcp is enabled, it should automatically assign your device a new IP. These often expire after a certain amount of time. You'll need to do what was latterly. This page should help you in setting up DHCP. [ Register or Signin to view external links. ]

You didn't specify as far as your router type, so I can't offer an exact step-by-step tutorial on how to enable your dhcp. If the latterly posted thread does not help you, then I recommend you to use a search engine and enter "How to enable DHCP on a (router type here)". Other tips: Refer to your product manual for instructions for your specific router. You should be able to follow this as a rough guide for most devices. The basics are all the same, only the actual location within the router software is different.

Warnings about enabling dhcp: Enabling DHCP on an unsecured wireless network is a big no-no. Doing so enables anyone to connect to it without any knowledge of networking and steal your bandwidth. Make sure you have physical access to your network device in case you have to reset it back to factory defaults.

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The "Error: Can't obtain an IP address from your router or modem" Xbox LIVE support page may serve some use in helping you resolve your issue(s) it can be found here: [ Register or Signin to view external links. ]


Have a good one,
Phosphor

i had this problem with my old router, their is an easy way around it, on the xbox when it says can't obtain ip just go on more info and maybe again... then it tells you to go to a website... something like xbox.com/ipadress that might not be it :L then you just follow the steps and all i had to do is type my xbox ip manually and it worked fine. then all you have to do is connect to xbox live everytime because for some reason it doesn't connect automatically.