Ethernet port not working after Yosemite upgrade.

Before I upgraded to Yosemite the Ethernet port on my iMac was working fine. After, not at all. It says that my cable is unplugged but it is not. My airport works with the same cable and ethernet at wall so it can't be the 'device at the other end' (i.e. router). Is there a fix for this? I am able to use WIFI but would rather be hardwired. HELP!

Thank you in advance

Susan