I was so happy today that I have been finally able to install Windows Phone 8 SDK and try it a bit. I installed fresh new installation of Windows 8 Pro into my virtual machi
Edit: Oh, I didn't noticed that you are trying to run emulator on VM. My answer is for non-VM environment.
First of all, you need to check hardware requirement at here
Be careful, successful installation of SDK does not guarantee "your hardware is compatible" If your hardware is compatible and Hyper-V is running(described in the link above), please check your BIOS and be sure to enable hardware virtualization in CPU Configuration
(for me, I could find it at Booting > BIOS > Advanced > Advanced > CPU Configuration)
Brief summary: