Vostro 1520

I've had this laptop for about a month and the network connection (cabled to 4 port router) has worked perfectly. This morning I turn it on and it insists the network cable is unplugged... I've checked the cable, checked the router, checked the connection, checked all the settings I can think of and it still says network cable unplugged. An ipconfig command returns the error media disconnected.

Maybe I'm overlooking something simple or maybe there's a fault .. I'm out of ideas... but it's been working perfectly with no changes for all that time and suddenly this happens.

Help?  Please??