About iTunes Store authorization and deauthorization
You'll basically need to deauthorize all computers on your account and then authorize the ones you're still using.
You won't even have the option to do this unless you have 5 machines authorized and you can only do this once every 12 months.
I guess it's because otherwise you could just deautorise and then autorise any time you wanted to use a different PC/Mac, which would be a get around for the DRM.