To virtualize the server using the Hyper-V solution, in order to save time and improve security, install Windows Server 2012 directly as Microsoft Server 2012 Core. After installation, only a cmd command prompt is available. Managing the server is inconvenient, so consider switching to GUI mode and then switching to Core mode.
To switch to GUI mode, manually install the GUI components of Windows Server using the Install-WindowsFeature and Uninstall-WindowsFeature commands to install and remove Windows features.
Execute the following command in PowerShell to complete the installation of GUI components. After completion, restart the server to switch to GUI mode.
Install-WindowsFeature Server-Gui-Mgmt-Infra Server-Gui-Shell –Restart
Execute the following command in PowerShell to complete the removal of GUI components. After completion, restart the server to switch to Server Core mode.
Uninstall-WindowsFeature Server-Gui-Mgmt-Infra Server-Gui-Shell -Restart
If you prefer using Server Manager, you can go to Server Manager -> Features -> "Graphical Management Tools and Infrastructure, Server Graphical Shell" and deselect it, then restart to switch to the Server Core interface.
Reference: https://technet.microsoft.com/en-us/library/jj574091(v=ws.11).aspx