You cannot open Dashboard until the Windows Server Essentials configuration is complete:

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You need to open Server Manager and allow the Server Essentials installation to complete.

Then in Server Manager go to Windows Server Essentials in the left pane and you will see a yellow bar at the top prompting you to complete the installation as per:



Then you will see the screen to configure Windows Server Essentials role:



The configuration takes a while and then it is done:

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