You may need to authorize the computer for the correct iTunes Store account.
Authorize using the correct account name
The items you are trying to play might have been purchased using a different iTunes Store account. To determine which account was used to purchase an item, follow these steps:
- Select a purchased song in your library and choose File > Get Info.
- Click the Summary tab. Note the Account Name that appears in the list. This is the account name (Apple ID) you will need to use when authorizing your computer to play this purchase.
Note: The account name that appears is the one you used when purchasing the item and does not change if the account name (Apple ID) changes.
If you've authorized the Apple ID that is shown in the Summary tab, you can check the purchase history for that Apple ID from Store > View My Account. If your purchase history does not reflect the purchase of the items in your iTunes library, consider any other Apple ID you may have created, and authorize the computer for your additional Apple ID.
If you forgot the password to one of your accounts, you can recover it using Apple's password-recovery website.