Check in Device Manager if your network interface card (NIC) has been
disabled. A red X will be present if the card is disabled. If so right
click it and select enable.
Are you trying to network 2 or more computers in the same house? If not, go
to Network Connections, right click on the lan icon and select DISABLE which
will stop that happening.
If you ARE trying to network 2 or more computers in the same house, is it
possible that you aren't using the wired port and may be using wi-fi and
expect the wired port to just say it is OK or something similar to that?
Doesn't happen that way, if so.