First, on your computer access your command prompt and type in ipconfig. Find the line called default gateway and write it down for later. Type your default gateway into your internet address bar and it will bring up your router setup page. Find your upnp and enable it, this will open your NAT. Start your XBox 360 and go to system settings on your XBox dashboard, go down to network settings and test your connection. Next go to IP settings then manual then IP settings. You want to change your IP address to 192.168.2.255 next go down to subnet mask and make sure it's 255.255.255.0 then click done, go to your gateway and change it to the default gateway you got earlier. Next you're going to go down to DNS settings. Click manual again and go to primary (you won't mess with secondary) and put in the default gateway that you wrote earlier.