Server 2012 Server Core powershell not installed

Use the Deployment Image Servicing and Management (DISM.exe) tool to enable PowerShell:

dism.exe /online /enable-feature /featurename:MicrosoftWindowsPowerShellRoot

...or if that's not enough:

dism.exe /online /enable-feature /featurename:MicrosoftWindowsPowerShell /all

dism.exe /online /enable-feature /featurename:MicrosoftWindowsPowerShellRoot
dism.exe /online /enable-feature /featurename:MicrosoftWindowsPowerShell /all

Say "yes" for reboot.

powershell
Add-WindowsFeature Server-Gui-Shell, Server-Gui-Mgmt-Infra
Shutdown -r -t 0

In server 2012 R2 Use Shutdown /r /t 0