Intel Virtualization Technology and VT-X won't work in Windows 8.1

For anyone who may still have this issue, I've successfully resolved it. The problem is caused by the fact that Intel Virtualization Technology and Hyper-V cannot run at the same time. There are several possible solutions, pick the one that best fits you:

1. Completely disable Hyper-V in your system.

   This can be done either by opening Control Panel -> Programs and Features -> Turn Windows Features on or off and then deselecting Hyper-V in the list, or via the command prompt by using the command:

   Disable-WindowsOptionalFeature -Online -FeatureName Microsoft-Hyper-V-All
   

   Note that this operation requires a command prompt with elevated privileges (i.e. admin mode). To re-enable Hyper-V, use the command:

   Enable-WindowsOptionalFeature -Online -FeatureName Microsoft-Hyper-V –All
   

2. Prevent Hyper-V from running on system startup

   This way may be more comfortable for those who occasionally need Hyper-V (e.g. for Windows Phone emulation). To prevent Hyper-V from starting automatically, use the command:

   bcdedit /set hypervisorlaunchtype off
   

   To re-enable automatic start, use the command:

   bcdedit /set hypervisorlaunchtype auto
   

   Again, this requires a command prompt window with elevated privileges.

    All of these commands require a reboot before they take effect.

I had a similar issue. VT-x features locked or unavailable in MSR. VERR_VMX_MSR_LOCKED_OR_DISABLED. I run the VMBox for years and not this... I checked all the Forums and nothing helped me, than I realised there was an update of my antivirus software. So problem came from the new AVAST antivirus software. In AVAST Options-> Troubleshooting->Disable Hardware Virtualisation

After a reboot I could start my VirtaulBox again, VT-x features were no longer blocked.

I hope this post help some of you too.

Greetings Martin