Connect to your files via FTP, then add lines about the debug in wp-config.php as described in the mentioned article. Then re-create the problem to be able to see if any new lines with texts of errors appear.
Provide us with temporary wp-admin and FTP access, so we can check the problem more deeply.
If you don’t know what the FTP is then you need to contact your hosting provider. Hosting support knows.
Regards