You don’t say which motherboard you have. That helps the helpers.
Which model, are you using a built-in Ethernet or one from an add-in card?
It may just be that the driver is incorrectly installed - often the case on this forum.
Go to the Control Panel and click on “Device Manager” and then look for “Network adapters”, click on it.
You are looking for the one that does not say ”WAN Miniport”.
It may have an exclamation mark (!) on it.
Alternatively you may see something under “Other Device” with the exclamation mark.
Which ever unistall it and reboot your computer.
Go back and look in the “Device Manager”. What do you see?