RDC Black Screen

I can remote desktop into my Windows 2008 R2 Server on initial install.
After activating Hyper-V I cannot connect to the Windows 2008 R2 Server.
It provide a black screen on the RDC if I set the Network card under Hyper-V to External

Once I setup a Virtual Machine, I can remote desktop into the virtual machine OK but not the Main Server.

Unsure as to what further information you require.

Thanks