If you would like to test out Windows Server 2012 Hyper-v within VMware Workstation then you may have come across this error message when trying to enable the Hyper-v role.
Hyper-V cannot be installed: A hypervisor is already running.
In order to resolve this you will need to shutdown the Hyper-v guest vm and make the following changes:
1/ Edit the settings of the vm and ENABLE Virtualize Intel VT-x/EPT or AMD-V/RVI
2/ Then open the VMX file with notepad for the hyper-v virtual machine (which will usually be located with the vmdk file in “c:\users\vhorizon\documents\virtual machines\hyper-v\hyperv.vmx” for example, then add the the following 2 lines to the bottom of the vmx file.
hypervisor.cpuid.v0 = “FALSE”
mce.enable = “TRUE”
All you need to do now is start your virtual machine and add the hyper-v role.
Author: Dale Scriven