Detecting service message on Nighthawk MR1100

The router constantly shows a message saying "detecting service". I can connect devices to it but not getting onto internet or if i do its very slow and usually times out. Took to telstra shop, first time they said it was a faulty sim card so changed that, no difference, went back and they said, "i can connect to it so it seems to be working fine". The bar on the right hand side that shows signal strength has been blank since the detecting service message appeared. All updates done, factory reset done. Does anyone have any ideas to help me get reception back please