Need help with router not connecting to Xbox


#1

Previously my router had 2 ports being used because I only had 2 ethernet cables.
So I had each cable attached to a computer, but to use my PS3 or XBox, I had to disconnect one computer cable and plug it into the system, which worked fine.

Now I bought another cable so that I could just alternate the systems connectivity and not unplug any computers.
However with the 3rd cable, the Xbox does not recognize any sort of connectivity. Which is weird because I was using it online just a few days ago.
I tried it to the PS3 and it was fine.

Is it possible the modem on the Xbox fried for some reason in a matter of 4 days?