Does your ISP device show that it is in proper working order, or are some lights on it blinking slowly indicating an issue?
Shutdown your computer, your router, and your ISP modem in that order. Wait ten minutes. Power them back on in reverse order, waiting for the each network device to be fully booted and running before the next. Then power on your computer.
Do you now have a usable network connection? If you have not made internal cabling, switch, or other changes to your router settings, then it might be worthwhile to ask your ISP support team to check the network integrity to their premise ISP modem at your location. They may also be having network infrastructure issues of their own.