Don, assuming you have double-checked the ethernet cable from the desktop to the router, I suspect Windows 10 Automatic Updates has updated the driver for your LAN adapter and that's why it worked initially but is now failing.
I don't have a Win10 system to be able to guide you directly to disabling the hardware.
In 8.1, you would open the Network and Sharing Center and there would be a link on the left to Change Adapter Settings. Right click the disconnected ethernet adapter and "disable". Reboot and see if that cleans up the Wi-fi connection.
If that works, then we can start looking to get your ethernet working again.
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