Wired Ethernet connection not working

The cable, router port, adapter or an internet outage may be responsible.

Do not factory-reset a router speculatively or indiscriminately disable Wi-Fi security or a firewall. Get permission before changing someone else’s network.

Check the cable at the device and at a LAN port on the router. Do not confuse LAN with the WAN/Internet port.
If possible, try another undamaged Ethernet cable or LAN port. Do not change cabling on someone else’s workplace network.
Does Wi-Fi through the same router work? If not, first check for a provider or router outage.
If only one PC is affected, restart it and check whether Windows lists the network adapter. Do not enter static IP or DNS settings without appropriate instructions.

Test after each step and stop when the issue is solved. Checkmarks are not permanently saved.