FingerTester, I know how frustrating it can be as I had the same issue. A hard factory reset did the trick as recommended by Netduma Fraser. Just to verify, did you you follow the steps below:
To hard reset your router, you’ll need a paper clip like object.
Use the paper-clip to hold the reset pin on the back of the router for at least 30 seconds. After 30 seconds release the paper-clip. Leave the router alone for 5 minutes. Access the interface once again and complete the initial setup process.
Good luck on getting up and running…Dave