Cisco WRT54G2 only Ethernet (modem) Port Not Working

Seems that my Cisco WRT54G2 is half dead, he connects both cable and wifi, transfer files between PCs it normally, but the router does not connect to the Internet by modem. When I connect the PC directly into the cable modem, it works.
Does only the router port that connects the modem burned? All other ports function properly.
I tried to update the firmware on the router and was successful, but the problem is still the same. The modem looks normal, only the wireless signal it has problems, but this crap Motorola has problem of wireless signal since arriving.
Please anyone has an idea, I'm grateful, I'm almost buying another router, just want to know if this is salvation before throwing $ out.

SOLVED

I was able to speak with staff support from Cisco.
It's a problem somehow common.
First, to test if the router has a problem treasury, just pick up the network cable and plug one end into the other ethernet port 1, then 2, etc.. If all of them light up, your router is alive, is just setting or update only. In my case just replace the latest firmware solved the problem.
Hope that helps anyone who has the same problem.