Computers stopped connecting to my Nighthawl X65AC3000

Well my enthusiasm was short lived. When I tried to manually connect all went well until it asked me to put "mywifiext.local" into the browser and it said it was an incorrect location. I tried the other suggestions with the same result and even put in the IP of the extender to no avail. I noticed, however that the signals on the front of the extender showed full connection so put it in place on the upper floor and it showed a 5 bar connection on the extender but when I tried to search the interneton the PC upstair it would not connect and told me I had to finish the connection procedure so I ended up back where I started.

I can just reach my main router from the upper floor so I know my computer is fine and my internet connection to the building is fine. The extender shows as fully connected (as I went back to using WPS to try and connect) but whenever I actually try to connect it says I have not completed the installation even though the procedure won't let me go to the final phase.

Before I give up and bin it, are there any other suggestions please?