Quick Fix: You have to reset the router back to its factory
default settings. You'll lose all your configuration settings made on
the router. On the back of most routers is a recessed button labeled
"Reset." Using a paper clip, hold this button in until the LEDs on the
router blink (the amount of time you need to hold the reset button may
vary from router to router, so check the documentation). This will reset
the router back to factory settings, enabling you to use the default
username and password again. Also, many current routers allow you to
save the configuration settings so you don't have to reconfigure after
performing a factory reset, so check to see if your router has that
capability. Internet Connection Tips; I Forgot the Password to My Router