I would try another cable, just in case and try another port on the router. Try locking the network card speed at a different speed and see if it picks up the link.
To change the network card speed. Go to Control Panel>Network Connections and right click on Local Area Network and go to properties, you will see your network card listed on top, click on Configure>advanced and look for link speed and duplex or something along those lines. It will give you the option to change the value from Auto-Detect, 1000mbps/full, 1000mbps/half, 100mbps/full, 100mbps/half, 10mbps/full and 10mbps/half. Change the speed close the properties and see if you can pick the link up. If not have you tried using the latest drivers from the NIC?
To change the network card speed. Go to Control Panel>Network Connections and right click on Local Area Network and go to properties, you will see your network card listed on top, click on Configure>advanced and look for link speed and duplex or something along those lines. It will give you the option to change the value from Auto-Detect, 1000mbps/full, 1000mbps/half, 100mbps/full, 100mbps/half, 10mbps/full and 10mbps/half. Change the speed close the properties and see if you can pick the link up. If not have you tried using the latest drivers from the NIC?