|This could be one of a few things.........so here's what I'd look at:|
1) Ensure NIC is enabled and working in Device Manager
2) Ensure cable is good. If you have another cable you know is good, try it to test
3) Ensure LAN port in router is not bad by plugging cable into another LAN port on router
If the NIC looks good and is enabled and the cable and port are good, the last thing I'd try is uninstalling, then reinstalling the TCP/IP stack on the NIC.