Admin Dashboard forbidden message?

Hi,

We have a working WP site and recently noticed that don’t have access to admin section.When we click dashboard or any other admin link it says Forbidden!

200% sure that username and password is correct.Reason once we logged in as admin for some reason it shows admin menu bottom of the page (front end) meaning admin login was success but all links gives forbidden message.

Tried to reset the files and folder permissions, reset htaccess but nothing helped.

Can anyone tell us how to fix this issue and reason for this.

Thanks