Drupal Help / 500 Error & Password Issue -- 2

I have a drupal project that has been running for some time. I was notified recently that one of the function on the website wasn't working. I went to login and am getting 500 error getting to the admin panel. Come to find out we don't have the password credentials correct either. I need someone who can get in via / SFTP & cpanel to troubleshoot, update and resolve whatever is causing the 500 error, as well as reset the users credentials for the site so we can access it. Must be able to start asap