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For more information on this, take a look at:
iTunes Store: Authorize or deauthorize your Mac or PC
To authorize a computer, follow these steps:
- Open iTunes.
- Choose Store > Authorize This Computer from the menu bar.
You may need to show the menu bar to see this option in Windows. In earlier versions of iTunes, you can access this option from the Advanced menu.
- Enter your Apple ID and click Authorize.
If your Apple ID uses an expired MobileMe account, you can still authorize your computer.
In some cases, iTunes may ask you to authorize the computer again. iTunes should use the same authorization as before if the computer is in your list of authorized computers.
Learn what to do if iTunes repeatedly asks you to authorize when you try to play your content.
Best of luck,