In this case we would suggest you to try using the default login credentials if this is the first time that you are accessing GUI then you can use the default login credentials as Username : admin and the password : motorola / password in lower case. If this doesn't work you can try resetting modem then try again with the default login credentials.

To reset the modem follow the steps below:
At the back of the modem, in the middle section you will see a small hole, inside that hole there is a button, and that is the reset button, please insert a paper clip or a tip of a pen and hold it for 15-30 seconds until all your lights go off, afterwards wait until your device fully boots up.

But after resetting the modem will go to default setup any custom settings will be removed so use the default network name and password to connect to your network.