Ran into this error when trying to start my Virtual Box VM: VT-x is not available (VERR_VMX_NO_VMX).

Turns out, enabling Hyper-V on a Windows 10 install messes with Virtual Box (or something). Seeing how there is no real need to run Hyper-V and Virtual Box, I simply disabled Hyper-V (reboot required), and the error went away.

Guess Microsoft and Oracle still can’t get along.