Connected, but no Internet connection. I have to reset router every 5 min, get access, then its gone

Have Fibre coming into Zyxel router. For a week now, i have connection, but no internet connection. i do factor reset, i get connection for 5 min, then its gone. Today, unplug everything, wait 5 min, connect power and fibre and nothing at all, not even on reset. Help. Frustated. No nothing about routers.....