We'd like to have a view of your setup.
Are you able to post a picture of the cables connecting the NBN NCD box and the router?
Did you just unplugged the Archer router or both Archer and NBN NCD box?
Alright. Since you have an NBN ARRIS NTD box, you are under the NBN HFC technology.
The lights on the NBN NTD box should be solid, if it's flashing, then something is wrong or else it is taking some time to regain the connection from the server.
Kindly send us a private message with your account details for further checking.