Make Tech Easier shows us how to get up and running with VirtualBox from a bootable USB drive. To do this, you'll need a bootable USB drive (obviously) and you'll need to be comfortable using command ...

The "Bootable" legacy ISO you've used is in fact not bootable, it relies on CDROM emulation provided by BIOS. VMs don't usually do this sort of emulation. If you set the guest OS to something like ...