I spent some time fixing this on a Dell Optiplex 755. I thought it was a BIOS update that was necesary and had to hunt for a DOS bootable that could run the EXE given by Dell. FreeDOS wouldn't work. Finally found a disk given by Dell (with some other machine) that was a bootable. Even the updated BIOS didn't solve this issue.
I then searched around the net and found this post that mentioned to disable Trusted Execution. Well, if you have an option that enables virtualization and then give another option that effectively disables it, what good is this UI?
This, however, sounds like something that I don't yet understand. So I should go read what that is and how to make KVM run with it enabled.