Q: Our old computer crashed, but thankfully before that happened we had copied the whole library onto an external hard drive. I now have a new computer, but I’m worried that when I transfer the music onto the new computer, it won’t be connected to my same Apple ID. This is important because I have money from gift cards in my old Apple ID account and I want to make sure everything is together again so I can lift it all to iCloud and iTunes Match. How do I make sure my recovered music is still under my Apple ID account?
A: Content purchased from iTunes is always tied to the Apple ID used to make that purchase regardless of the computer that content is loaded onto. It is essentially impossible for your music to be connected to a different Apple ID even if you wanted it to be—it’s your computer that will need to be configured for the Apple ID associated with your content, not the other way around.
For copy protected content such as movies, TV shows, books and older music purchases you are required to authorize your computer for your Apple ID in order to play that content. Music purchased since 2007 and all music purchased since mid 2009 is not copy protected and no authorization is required to play that content or transfer it to an iPod or iOS device, however you should use the same Apple ID to sign up for iTunes Match as was used to purchase your content. This will ensure that your previously purchased content is available automatically from iCloud rather than having to go through the process of attempting to match or upload it.
iTunes will actually prompt you for authorization the first time you try to play a copy-protected item in your library, but you can authorize your computer manually simply by choosing Authorize This Computer from the Store menu in iTunes.
You can have up to five computers authorized at any time for a given Apple ID. If you’ve reached this limit, you can either reauthorize another computer using the Deauthorize This Computer option on the iTunes Store menu, or you can reset all of your computer authorizations by going to your iTunes Store Account Preferences by choosing View My Account from the Store menu in iTunes; an option will appear on the main Account Information screen showing you how many computers are authorized for your Apple ID with a button to deauthorize all of your computers. This option can only be used once per year and will only appear if you have two or more authorized computers on your account.
After doing this you will need to manually reauthorize any computers that you wish to continue using with your Apple ID.