Enable RDP on Hyper-V Server Core

Windows Hyper-V Server Core, is a free Hypervisor that runs on top of a stripped down, CLI-based version of Windows Server 2008 R2.

You should enable remote desktop (RDP) because, curiously some commands don't work using remote tools using a PSExec.

You can however enable RDP on Server Core remotely using a tool such as PSExec

Cscript %windir%\system32\SCRegEdit.wsf /ar 0
Cscript %windir%\system32\SCRegEdit.wsf /cs 0

source: http://support.microsoft.com/kb/555964