Screen frozen on "Starting Windows" when building Server 2008 on Server 2012 Hyper-V

Symptom:

When trying to build a Windows Server 2008 (R2 in my case) on Server 2012 R2 Hyper-V, the VM would not get past the 'Starting Windows' screen.

Fix:

Recreate the VM in Hyper-V and ensure 'Gen 1' is selected ('Gen 2' will only work for Server 2012 +)