I'm running Virtualbox 4.16 under 12.04. The machine is a 12.04 install as well. It works perfectly fine under windows 7... where it was created as Ubuntu 64-bit. But when trying to run it under Ubuntu 64-bit (same version of Virtualbox) it won't load.

Checking the info panel while it's running shows that VT is disabled... even though it is enabled in the bios (I repeat: IT IS ENABLED IN THE BIOS).

It boots, gets to the screen where you choose whether you want to run in safe mode. Then just sits frozen at either a "_" or just a blank screen.

Networking is configured properly.