Unable to start the Windows Phone Emulator

I've seen this error several times. Each time I google deeply and finally made me reinstall my windows and all stuffs. Please help, I don't want to reinstall everything again. The error is:

Windows Phone Emulator

Unable to start the Windows Phone Emulator

Windows Phone Emulator is unable to start because 
the hypervisor is not running. The likely cause is
that hardware-assisted virtualization is not enabled.

Check your computer's BIOS to ensure that hardware-
assisted virtualization and hardware-assisted data 
execution features are enabled.

But yesterday I debugged really normally on Windows Phone using Emulator and I really sure
I've turned on Virtualization in BIOS and also in Turn Windows features on or off :

Sometimes when I hit f5 the IDE come with another error: 0x80131500

My PC: windows 8.1 ultimate 64b, 4gb ram, i3, Visual Studio 2013 RC3

Finally after struggling all day, I solved it ^^ I post the solution here so that somebody don't have to waste time just like me to solve such a silly error!

Just simple disable Hyper-V option in Turn Windows features on or off (you could open this by hit the combination Windows + S, this will open the search box, then type "Turn Windows features on or off"
restart your PC
enable the Hyper-V option by using the same way as step 1.

Enjoy coding :D

If the accepted answer doesn't work for you - as it unfortunately did not for me - also be sure to enable Data Execution Prevention (DEP) in your BIOS.

The article below outlines what BIOS settings to enable for Hyper-V: https://msdn.microsoft.com/en-us/library/windows/apps/jj863509%28v=vs.105%29.aspx

In my case, I had hardware-assisted virtualization enabled in the BIOS, but not data execution prevention (DEP). I also had Hyper-V enabled via Windows Features. After enabling DEP in the BIOS, I was able to run the Windows phone emulator.

CMD with admin rights: