Unable to get ethernet working on a new BT Home Hub 4
I have recently had a BT Home Hub 4 and can get WiFi without any problem but unable to use my iMac through a ethernet connection.
All the tests and checks say it is connected by ethernet , but if I switch wifi off and try to use a ethernet cable it says I am not connected.
I have also tried a laptop with a ethernet cable into the BT Home Hub and it works fine.
So It looks like something has changed on my iMac which is preventing me using a network.
Any help would be much appreciated
iMac, OS X Yosemite (10.10)