Xbox 360 isnt connecting to the internet but my computer does

SOURCE: my wireless XBOX 360 says ''not connected'' when I test XBOX LIVE

hi,
in this case you need to do a port forwarding,which is something like opening the specific ports on router so that xbox will communicate with internet
for that we need to know the ip address of xbox and port numbers for xbox.contact microsoft for knowing the port numbers and their range,so we can do a port forwarding on your router

SOURCE: Dlink allowing Xbox 360 to connect to Xbox Live

Yep. No problem. Step by Step right here.

http://portforward.com/english/routers/port_forwarding/Dlink/DI-624/Xbox_Live_360.htm

SOURCE: How do i change my NAT connection from moderate to open

This one is simple. Find the IP address that your Xbox is assigned by your router, then put it into the DMZ. This also goes for PS3 users who are having trouble with internet access.

SOURCE: cant connect to xbox live

make sure that your xbox is acctually getting an ip address, by default it should be a 192.168.0.xx number and the gateway should be 192.168.0.254
If however your xbox tells you that its ip address is 168.xx.xx.xx (a private ip address) or if it is simply 0.0.0.0 it would sugest a cabling problem.
However if the network troubleshooter finds no faults and you are still unable to get into xbox live try setting up a PPPoE connection using the username eircom and broadband1.
Alternatively,If you click on Firewall in the Netopia admin page, and set the security level to Low, xbox live would suddenly start to work.
******Also add UDP ports 88 and 3074 if nothing works.On a netopia 3347 you can get this option in the NAT option.U have to enter the port numbers and the service name(xbox).
Hope it works for you.

SOURCE: Can't connect to Xbox live but internet test passes

u tried updating the firmware