- Check if you accidentally deleted the wp-login.php file on the document root, if so copy it from another wordpress installation & paste it back.
- Just over write the wp-admin file with a fresh installation preferably from a fresh wordpress installation of the same wordpress version.
- Delete the .htaccess file and try accessing the backend dashboard again, if it’s fixed then try copying the .htacess contents from another wordpress site.
Thought I could write on this common wordpress issue (When accessing wp-admin returns wp-admin 404 error!); everything else seems fine with the front end usage i.e all front end users have no complaints but you the wordpress site admin has all complaints at hand. You just can’t access the wp-admin (administrative dashboard) with this wp-admin 404 error all over in your eyes and messing up your mind, here is what I checked out and this could help you out in troubleshooting too;