Stop hyper-v service running by default in Windows 8/10, since it blocks all other calls to VT hardware.
Additional explanation here:
https://social.technet.microsoft.com/Forums/windows/en-US/118561b9-7155-46e3-a874-6a38b35c67fd/hyperv-disables-vtx-for-other-hypervisors?forum=w8itprogeneral
Also as you have mentioned, if not already enabled, turn on Intel VT virtualization in BIOS settings and restart the machine.
To turn Hypervisor off, run this from Command Prompt (Admin) (Windows+X):
bcdedit /set hypervisorlaunchtype off
and reboot your computer. To turn it back on again, run:
bcdedit /set hypervisorlaunchtype on
If you receive “The integer data is not valid as specified”, try:
bcdedit /set hypervisorlaunchtype auto
— credit Tj Kellie