The Plesk Home page shows a blank page or "500 Internal Server Error".
The log file
/var/log/plesk/panel.logcontains the following message:
CONFIG_TEXT: PHP Fatal error: require_once(): Failed opening required 'modules/firewall/FwConfigurator.php' (include_path='/usr/local/sb/include:/opt/psa/admin/plib:/opt/psa/admin/externals:/usr/local/sb/include:/usr/local/sb/include/PEAR') in /opt/psa/admin/application/admin/controllers/HomeController.php on line 104
`FwConfigurator.php` is a part of Plesk firewall module, but this was not properly installed.
The Plesk Firewall extension is corrupted.
Re-install the Plesk Firewall extension: How to install / uninstall Plesk components?