Forbidden entry to my router IP address

Hi dear all, I am trying to reset the password of my buffalo router by entering the Ip address: 192.168.11.1. However, after a few attempts(I changed a few things such as the user name and Ppoe password, then the page start loading , I can’t log in the page again.) when I tried again, the page gone blank and state ‘Forbidden You don't have permission to access this resource.’

Now I still can not reset my router password and access the wifi.

Anyone can tell me why would that happen snd what should I do?