Cannot Access Back End

Hello all, this is my first question. I am trying to log into the back end of my site but cannot.

the bestwebsoft google captcha is not displaying. any attempt to log in returns a wrong username or password message.

i have googled this problem and a few have said to rename the cpatcha plugin via file manager which i tried but the problem still happens.

the site runs the storefront theme with minimal plugins.

can anybody explain how to resolve this issue please and thank you