Do you have access via FTP or SFTP? If so you could test disabling all plugins. To do that go to /wp-content/plugins/
Inside the plugins directory create a new directory calle off and move all plugins inside the off directory. See if you can access the login page now. If not you can try the same thing in /wp-content/themes/
to see if it’s a plugin or a theme causing that.
Other thing to try is to find the .htaccess file in your root folder and rename it to disable it to see if that is causing this behavior.