Hi,
The Physical Address/Host ID, is the address that is assigned to your network card. These are generally hard coded, so it is unlikely that this is changing (unless you are using a VM - even then, once a Hardware ID is assigned, it doesn't change automatically).
It is possible that you may be running off different network card adapters, especially if you are using a laptop (i.e. wireless card or ethernet card).
In some cases, when you plug a network cable in, it can disable the wireless adapter, therefore disabling any licenses that may be attached to that Hardware ID.
I don't know enough about the student version (Express?) to understand how it is licensed, but i would be inclined to establish what network card you were running when you installed it and it worked and see if you can go back to that configuration. If this works, then you need to be sure that Hardware ID is not disabled whenver you want to run Modeling.
Hope that helps?
Thanks
Barry
