Q: I installed iTunes on a new laptop while my old laptop was being “de-virused.” Inadvertently, I used my email address as my iTunes (Apple) ID instead of the old ID. Now it won’t play any of my music. How do I change the new Apple ID back to the old Apple ID?
A: You actually don’t need to “change” the Apple ID back over, but rather simply authorize your computer to play music from your original iTunes Store account. Normally iTunes should prompt you to enter your iTunes Store username and password whenever you try to play a protected item, but you can also bring up this dialog box directly by choosing Authorize Computer from the “Store” menu in iTunes. In either case, you’re presented with a dialog box asking you to log in to the iTunes Store.
Simply enter your old iTunes Store ID and password and iTunes will download the necessary information from your account to authorize the computer to play your existing music. Note that you can have more than one iTunes Store account authorized on the same computer, so you don’t specifically need to worry about removing the ID with your e-mail address. If you want to do this, however, you can Deauthorize your computer for a given iTunes Store account by choosing Deauthorize Computer from the Store menu and entering the username and password for the account you want to deauthorize from iTunes.