I would suggest try setting the duplex to Auto. Of it its on auto already, try 100Mbps
From the routers access page:
Advanced> Advanced Network> WAN port speed to Auto or 100Mbs
Also, try hooking up a ethernet port from the WAN to the PC. You might not get a IP, but you should atleast get connectivity. That will test for a bad port. Also, see what the status page says. If the router isn't configured correctly to get a IP from the Modem, or the modem isn't configured correct to give a IP to the router, you can have a problem. Ofcourse, also try a full power cycle. Make sure the modem is 100% online before turning on the router.