I noticed once on one HP server, after installing Hyper-V, that virtual workstations are not being launched, giving the following error:
Hyper-V Manager
An error occurred while attempting to start the selected virtual machine(s).
…
Virtual machine could not be started because the hypervisor is not running.
…
As it turned out, the problem was in the Intel (R) Virualization Tech not activated in BIOS, after changing from “Disabled” to “Enabled” and start the system, the virtual workstations were successfully launched.