Did you tried user name as "admin" and password as "password"? If you have changed it and it you are sure that you are trying the correct credentials, reset and reconfigure the extender.
I did a hard reset. The light blinks and it does not work after. Then I let it match with the main router via WPN it works. I am trying to link it via ethernet and to do that I must be able to log in.
Since you have already completed setup using WPS, try to login to it using mywifiext.net or IP address which your router assigned to it to access its settings. But, internet should be working already if setup was successful using WPS.
