Unable to activate Hyper-V on Windows 8.1 pro x64

Hi there,

I tried to activate Hyper-V on my desktop :

1. Add/Remove Features

2. Add Hyper-V, and all subsets

3. Click OK.

4. Click Restart when prompted.

5. Computer will reboot and then work on configuring features.  I got the error message "Unable to add feature...".

My configuration :

MotherBoard : ASRock Z77 pro3

Processor : Intel I5 3570k

RAM : 8 Gb

OS: Windows 8.1 pro x64OEM fully activated and updated.

I checked with intel processor identification utility, and my processor support SLAT (VT -x) and Intel virtualisation. I checked too with some tools (coreinfo, systeminfo), everything is ok..).

I updated my BIOS and activated the Virtualisation option.

No way to make it work..

Can anyone help me ?