After an upgrade or simply after rebooting a discover or detection server, the enforce console shows the server as starting.  The server stays in 'starting', while never actually showing as started in Enforce console.  Checking the discover servers directly shows that all services are on and things seem to be functioning properly.   

Sometimes the Enforce is 'out of sync' with the discover server. 

Simply restart the Enforce server. 

This will reset the reporting and show the true status of your connected servers.  If this does not work, check your discover / detection server logs for errors or warnings, and search this knowledge base for those errors or warnings for further assistance.