Could well be that the system has a hidden partition which is being used to store your operating system for recovery purposes. However, I double this would take more than a couple of GB and you seem to be adrift by 30 Gb. But it could be that the balance simply hasn't been formatted as a virtual drive.
Check what you system says when you first boot - should give the HDD model, and see what that indicates. Also, if you have something like Partition Magic, you can see what else is hidden on the drive.
Whatever you do, don't open the box, as this could invalidate any warranty. If software cannot answer, I would challenge the supplier for an explanation.