No wired internet - split topic

I have a Dell Dimension 8200 with a CNET Pro WL200 PCI Fast Ethernet Adapter. I also have a Linksys WRT54GX2 wireless router. When I connect the comp to the router with an ethernet cable(to any of the 4 ports) it shows 'network cable unplugged', the ethernet LEDs on the router are off and one NIC link light is green is color. But if I connect the comp directly to the modem with the same cable, I'm able to go online and both the link lights are on(one solid and the other blinking). I have a Dell laptop which is able to go online wired to the same router with the same cable with all the ports.

Edit: Split from older thread here: http://forums.whatthetech.com/index.php?showtopic=112333

Is the router setup to do MAC address filtering perhaps? The Users Guide has some good info on trouble shooting this problem. See here:

Wireless-G Broadband Router with SRX200 (WRT54GX2)

Look under Appendix A: Troubleshooting