Read this whole message before doing anything.
Back up all data.
Quit iTunes if it’s running.
Step 1
Hold down the option key and select
Go ▹ Library
from the Finder menu bar. Move the following items from the Library folder to the Trash, if they exist:
Application Support/SyncServices
Caches/com.apple.iTunes
Caches/QCCompositionRepository-com.apple.iTunes.cache
Containers/com.apple.BKAgentService
Saved Application State/com.apple.iTunes.savedState
Leave the Library folder open. Try iTunes again. If it works now, stop here. Close the Library folder.
Step 2
If you still have problems, quit iTunes again. Go back to the Finder and move the following item from the open Library folder to the Desktop:
iTunes
Note: you are not moving the iTunes application or the iTunes library. You’re moving a folder named “iTunes.”Test. If iTunes now works, delete the iTunes folder on the Desktop. Otherwise, quit iTunes again. Put back the folder you moved, overwriting the newer one that may have been created in its place, and continue.
Step 3
In the Preferences subfolder, there may be several files with names that begin as follows:
com.apple.iTunes
com.apple.mobile.iTunes
Move them all to the Desktop.
Also in the Preferences folder, there's a subfolder named "ByHost". Open it and do the same thing.
Test again. This time iTunes should perform normally, but your settings will be lost. You may be able to put back some of the files you moved to the Desktop in this step. Relaunch and test after each one. Eventually you should find one or more that causes iTunes to malfunction. Delete those files and recreate whatever settings they contained.
If the issue is still not resolved, quit iTunes again and put all the items you moved to the Desktop back where they were. You don’t need to replace the items you moved to the Trash. Stop here and post again.
If you later decide that you don’t like the results of steps 2 and 3, you can undo them completely by quitting iTunes and restoring the items you deleted in those steps from your backup.
