Internet is accessible through cable, but says no WAN detected when coecting the cable to the router

I coect my mac osx through a cable directly and it works fine. But if I plug the same cable on the router and coect the router through address 192.168.1.1, it says no WAN is coected. I've tried on Both of my routers which are all TP-LINK. On the router itself, the hint light is not on either. How could it be possible? Is there anyone who can give me some idea? Great thanks!