Cable Unplugged - iMac

I bought a new desk for my iMac today. I checked my email and then shut down my system from the Apple menu. I removed all the wires connected to the iMac and placed it carefully in the next room. Once I had the desk assembled I set up my iMac again. I could not connect to the internet via the network cable so I tried 2 other cables with no success. I then switched on Airport and was able to connect without issue.

I checked the network settings after switching off Airport and reconnecting the network cable and I get this message "Cable Unplugged - Either the cable for Ethernet is not plugged in or the device at the other end is not responding." From checking the forums I see this had been an issue for MacBooks. Is there a solid fix for this or do I need to go to the Apple store to get a new network card? I assume that this would be an expensive option.

Any help appreciated.