If you’ve gone through those steps, then the next ones are to reset the plugins folder – by renaming it to pluginsHOLD
– which will deactivate all plugins completely in case any are not fully deactivating the regular way.
Switch to a default theme while they are deactivated that way.
If still not working, you’ll need to manually (via FTP) replace all files and folders from a fresh download of WP EXCEPT wp-content, wp-config and .htaccess. Be sure to delete the old files and folders before uploading the new ones.