CANNOT setup router with gateway

I CANNOT get the gateway to work with my router, even in bridge mode. The routers IP address was not showing up and once the gateway was connected to the router, I could not get a connection. I tried power cycling both devices, resetting both devices and nothing resolved the problem. 

My setup was working. Then, all of a sudden. I became unable to access my routers login page. So. I replaced the router. Neither old nor new router will work now, with the gateway. 

Somewhere along the way, I became unable to access the gateway's settings too. 

How do I fix this?