It's possible the cable could be bad. If you have a cable tester, take the cable for a test to see if it's lossy or has any open pairs. It's possible your NIC/the router's switch happens to be operating in 10Mbps Full or Half Duplex mode, too. Could be a bad switch, a bad NIC, or some weird configuration issue with the PC for that specific network adapter.
Try another PC to see if you can isolate what the problem might be. That helps to rule out the cable and the switchport on the router.