It can occur that when your server operating system is updated you lose access to FileMaker Server and the FileMaker Server Admin Console. 

FileMaker's Support Methodology identifies the application as a factor to consider when troubleshooting an issue.  The most certain way to rule out the Server application is to perform a clean uninstall and reinstall of FileMaker Server. Follow the steps below to completely uninstall FileMaker Server while preserving your settings and data. 

This article will walk through the recommended steps

Answer Number: 000025757 Reinstalling FileMaker Server to troubleshoot an issue