The following items may not be displaying data in the Exchange 2010 Diagnostic Console:
Mailbox Store Size and Free space
Public Folders Size and Free Space
Transaction Logs Size and Free Space
WMI (Windows Management Instrumentation) Service is set to Disabled on Exchange Server.
Follow the steps below to fix the issue above.
1. Go to Start | Run then type in services.msc on the Exchange server having issues
2. Find the Windows Management Instrumentation Service and right-click on it and select Properties
3. Change the Startup Type to Automatic and click Start
4. Click OK
5. Open the Diagnostic Console and connect to your Exchange 2010 server and you will see data in those counters.