Hi SRS. I’ll start off by saying I’m making the possibly incorrect assumption that it’s just the network port on you motherboard gone. And it’s just something I might try. I can not advise on the Widow diagnostics or absence of.

If you did want to fit one, the first thing you would need to do is confirm what slots you have free on the motherboard. They might be PCI or PCI Express. Then you want a network card (PCI-e type shown)

Fitting should be easy.

Unplug the power and open the case. Touch yourself on something metal to discharge any static in you. The holes in the case for the slots will be covered by blanking plates and there will be some sort of screws or clamping mechanism but you will figure that out. Fit the new card that’s it inside.

You will want to move the network cable to this new socket and might like to try to disable the onboard network slot by looking around in the BIOS so you only show the one network card.

Configuration varies from system to system and I don’t know Win 10 well enough but if you are using DHCP (assign IP address automatically, commonly by the router), things might “just work”.