Does anyone know if it's possible (or necessary) to de-authorise one of the product keys that comes with MS Office (student/teacher edition). It comes with three keys, ie three licenses. The first key was used on my desktop machine which I shortly afterwards clean-installed, and I moved on to the second key (perhaps a silly idea in hindsight) for that re-install, then I put the third on my laptop. So the first key is no longer in use, but I need it for my new laptop. Can I just re-use it, or will Micro$oft know and not let me? Should I contact them? Has anyone successfully used a product key twice? I signed up for their silly Passport service (as I had to do to register the app), but there's nothing on there to manage my product registrations etc.