Start by testing your Xbox live connection with the following steps:
1. Start at the Xbox 360 dashboard.
2. From the My Xbox menu scroll to the far right to System Settings.
3. Choose Network Settings.
4. Select your connection type (wired or wireless).
5. Choose Test Xbox Live connection.
Performing the Xbox Live connection test
1. Turn off your Xbox 360 and your Modem/Router and wait for 15 - 30 seconds.
2. Fully power up your Modem/Router (it may take a couple of minutes to re-establish your connection).
3. Turn on your Xbox 360 and test the Xbox Live connection again by following the steps at the beginning of the article.
At this point if you still have trouble then you may have a firewall interfering with your connection. Please configure the following network ports within your router from your PC:
Example of port forwarding, this is done from your PC and will differ between devices
if this does not solve your issue, try placing your Xbox 360 in the DMZ of the router or establishing a direct connection to your modem and retry.
There may also be certain restrictions set by your Internet Service Provider (ISP). If you continue to have trouble, please contact your ISP for details on any specific restrictions on the previously mentioned network ports.
If you continue to have trouble after completing the above steps, please contact support and include a full description of your problem along with any error messages you may have received.