I recently backed up to CD music for my grandson. Deauthorized the computer (under my account) but didn't realize he also had an account on the same computer. I installed a new OS (Windows7), installed itunes the restored from the CDs. Now he can only play about half the songs. Some require him to enter an OLD appleID that was associate with the song purchased. When he enters the password, it says the AppleID doesn't exist. Any idea how to get the music to play again?