The virtual machine could not be started because the hypervisor is not running ...
this it what I was getting when trying to run a Hyper-V virtual machine on my HP ML380 server, a quick search and the problem was found : you have to make some changes in your BIOS (that means your CPU should support virtualization), you should enable two setting in BIOS :
1- hardware-assisted data execution protection (DEP) (was enabled by default for me)
2- hardware-assisted virtualization
and keep in mind that some machines does not apply BIOS changes until it completely turned off (just a normal restart wouldn't do it)
the real problem appears when you still get the Hypervisor error after applying these settings, here comes the solution:
the problem with me was "Persian locale", I uninstalled everything about Persian in "Region and Language" section in control panel, then uninstalled the Hyper-V and then Installed it when there was only English (US) on my system, after that everything goes smooth and alright