So you have changed your Windows Server 2012 GUI to Core if not you want to go here. Maybe you are on Core and want to switch to the GUI? This guide will help you get what you want.
Core is a great option, because it uses less resources and is known to have less security risk.
1. Open PowerShell from the Command Prompt.
2. Now type the following command and run it.
Install-WindowsFeature Server-Gui-Mgmt-Infra,Server-Gui-Shell -restart
3. Now you will see it start to collect data.
4. When it stops collecting it will give you a warning to restart. You do not have to do anything and it will restart for you.
5. Now it is working on creating your GUI feature.
6. It will give you the Windows Server 2012 splash screen.
7. It will come back with about 50% complete
8. Now you are on the GUI.