While playing with Vagrant, VirtualBox, and MongoDB on my old ASUS ROG Generation 1 - which has Intel Q720 CPU and runs Windows 10 64-bit - I ran into this error. VT-x is not available(VERR_VMX_NO_VMX). Also, VirtualBox list only 32-bit version for guest OS. It is so weird because I can installed Ubuntu 64-bit as guest OS in VirtualBox while booting this laptop in Windows 7 64-bit. I tried removing Hyper-V feature and reboot. VirtualBox now display 64-bit version of guest OSes. And Vagrant works too.