Because you asked, we're pretty safe to assume you have DHCP enabled in your router. It is a default setting with the kind of consequences that you'd remember disabling it.
Another thing to try is holding "M" button for about 10s. First you'll see slow blue blinking and then a burst of quick blinks. This will erase any WiFi credentials saved in the unit.
When I mentioned trying different router, I meant maybe a setup attempt at friend's or neighbor's house. Try that if practical, otherwise we'll just assume the router is fine.
If neither of above gets you through the setup, we'll try another unit.
BTW: You may be using an Internet provider supplied WiFi router that comes in a combo with the modem, but you can still use your own wireless router with that either as (better) primary access point or an range extender.