Fix VERR_SUP_VP_THREAD_NOT_ALONE, VirtualBox Error in supR3HardenedWinReSpawn, by following the solutions mentioned in this article.

If VirtualBox displays a black screen & is not booting the guest OS or not opening the installation window, you need to disable Hyper-V and 3D Acceleration.

One VirtualBox setting that is often overlooked is found under the System, Acceleration tab: Make sure both Hardware Virtualization boxes are ticked.