"Yeh i had this same problem to heres how you can check the problem which is probably your router. Go to the System Blade and test your Network Connection. At the bottom it says NAT. If it is strict or moderate then youll have ahard time joining rooms and communicating with other players. What you want is for your NAT to be open. If it is strict or moderate check this website to see if your router is compatible with the Xbox 360. http://www.xbox.com/en-US/live/connect/routerlanding.htm
You may need to just upgrade the firmware on your router. If that doesn't help you would need to open up your Router on the PC and open more ports. Heres how you would do that.
If you have a setting of MODERATE or STRICT you need to open 3 ports on your router.
I have called Microsoft and received the port numbers. They are as follows:
This will open the ports that the 360 uses.
To open the ports you will need to access your router via your PC and go to Port Triggering.
Label the post Xbox1 in the first address line, then imput 88 in all boxes, and finally click ENABLE.
Label the second line Xbox2 and imput 3074 in all of the boxes and finally click ENABLE.
You should not need to enter the TCP number because your router should automatically enable the TCP's.
Next, Cycle the power to your 360 and run the test again. At this point you should see your NAT at OPEN.
However if you router isn't compatible then you would need to buy a brand new one. They are currently on sale in a bunch of stores."