I think the only way to fix this is to reset the router. Power down the router before doing this. Most of them have a recessed button on the rear of the box. Typically you'll need to stretch out a paper clip and push the button in for ten seconds. This will reset the router to factory conditions. You'll need to look at your manual, but often the user name is admin and the password is blank the first time, then you can reset the PW. Write it down this time!