Cannot access backend suddenly

I have Hidden WP Admin installed on my WordPress site and when I logged out today, I received the following message when I clicked on my front end login link. The url that Hidden WP Admin is supposed to use is http://www.nycenglish.com/portal/ but it is giving me this message…

“Oops! That page can’t be found.
It looks like nothing was found at this location. Maybe try one of the links below or a search?”

I have had no problem with this plugin until today. Any thoughts? Thanks in advance!

https://ww.wp.xz.cn/plugins/hidden-wp-admin/