If you have changed any configuration or added PHP extensions / php.ini to Zend Server setup after installation,
try to revert your configuration and restart Apache.
If its a default, clean installation (not on an older version) - you can open a support ticket with reference to this forum post, and attach support tool output archive (from start -> zend- > zend server menu) to your ticket, for offline review.
If this is an installation on unclean machine, where an older Zend Server was once installed, you need to follow a wipe procedure like:
1. remove Zend Server
2. make sure there are no leftover PHP / Zend processes in task manager
3. rename (if you wish to maintain a backup) or delete the Zend directory (if you have MySQL, remove only Zend Server and Apache folders)
4. restart Windows
5. install a fresh copy of Zend Server 8.5.6 or 9.0.1 (PHP 7)
6. initialize from the web (http://127.0.0.1:10081
) and use the new installation, report back any initial problem