Help connecting Xbox through Ethernet

I'm at my friends house and he doesn't have Xbox live connected, and his whole house is pretty much set up wirelessly, but he doesn't want to pay $100 for the wireless adapter.

Here is a diagram of his home network setup



I've tried connecting an additional Ethernet from the modem to the other Cat5 port that the modem is connected to, or an Ethernet cable from the router into the same Cat5 port. For the life of me I can't get any sort of response on his Xbox, and it's not a router setting as it can't even find the router.

 

The modem will only allow one connection.

The router connects to the modem and allows several connections.

If you can't find the router, then you most likely don't have one LOL.


Umm, so you can unplug the cable running from the modem to the computer and connect it to the modem to the xbox.


I'd invest in a router if you want multiple workstations/xboxs running on the network.

 

I do have a router, It's right next to the modem. I was wondering how in the hell can I get on xbox live, the only thing that makes sense at this point is either faulty wires, or wiring, as the wires were installed when they bought the house.

I've connected an ethernet cable from the router into the wall, and then downstairs, connected the xbox to the wall via ethernet as well, nothing.

 

Is the PC connected to the router, and is it getting internet properly?

If not, then test if the router is working properly.

If so, then unplug the ethernet chord from the PC and connect it to the xbox to test if it is working properly.

If not, check DHCP settings on your router. Specifically if it is enabled or not.