Server Manager won't start in Windows Server 2012 R2

I had this issue after upgrading from 2008 R2 to 2012 R2.

Installing the latest version of .NET Framework (4.7) from Microsoft's website fixed the issue.

There is a user setting file at C:\Users\YourUserName\AppData\Local\Microsoft_Corporation\ServerManager.exe_StrongName_m3xk0k0ucj0oj3ai2hibnhnv4xobnimj\10.0.0.0\user.config. This file will be updated when user made any setting change on UI, and sometime this file can get corrupted because of crash or turn-off.

Try manually deleting the file and restarting Server Manager.