Q A week ago I updated iTunes. Since then, although all other sound output works fine, hitting the Play button in iTunes does nothing, and no sound emerges over the speakers connected to my iMac’s headphone socket. What is wrong?
A There do not appear to be similar issues reported with recent updates to iTunes, so it is most probably a problem specific to you.
First check the Equaliser in iTunes, toggling it to see if that restores sound output. Look for old or broken plugins, checking the iTunes folder inside each Library folder on your startup volume. Try restarting with the Shift key held down to disable third party extensions.
After those you should consider whether you iTunes library is broken. In iTunes, open Preferences and switch to Advanced Preferences to inspect the given location of the library. Ensure that you do not have a second copy of the iTunes app lurking on your disk, or a second library.
Next check your startup volume for errors, using Disk Utility. If all else fails you may need to rebuild your iTunes library from its component tracks and other files, or restore it from a recent Time Machine backup.
Updated from the original, which was first published in MacUser volume 30 issue 7, 2014.