iMac 2011 ethernet no longer working

The router and the ethernet jacks on the wall operate fine. The ethernet cable works just fine. The only thing that doesn't function is the ethernet functionality for the mac. When I plug directly into the router I see the light on the router light up indicating a connection, but when I go into the network settings section it says no ethernet cable is plugged in.

I am at my wit's end. I have looked far and wide and it seems like no one is having this problem.