is there WAN ip address on the router?
You mean you can still get internet via the modem?
try to restart your modem and router if the modem is still working properly.

Traced problem to computer turning off power to the modem at the UPS when the computer was shut down. Using a separate power source solved the problem.
Why it suddenly started doing this after running fine for months I've no idea, probably a software update.

Internet connection would not be connected because of the adapter settings and the plugins are not installed properly many times this is done because of the bug in the operating systems especially in the windows 10 so If any problem regarding of windows 10 then simply ping at Windows 10 Help and simply call back done from their side and also provide tools and software for for the betterment of the windows 10 operating system because this will improve the update part of the windows 10 in the system and also help to run smoothly as from the side of software side in c drive.