iTunes will not open

Try iTunes: Troubleshooting issues with third-party iTunes plug-ins - Apple Support.

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Download a fresh copy and install it. http://www.apple.com/itunes/download/

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What happens when you try to open it?

Apple Support has given the following instructions to others who had a similar problem.

First, back up all data.

Select the iTunes icon in the Applications folder and open the Info window. Click the padlock icon in the lower right corner to unlock the settings.

In the Sharing & Permissions section, change the Privilege setting for each Name in the list to Read & Write. Close the window. If the settings aren't visible, click the disclosure triangle on the left so that it points down.

You should now be able to drag the iTunes application to the Trash and empty. Your iTunes data won't be affected.

Click the iTunes link at the top of this page, download the Installer package and run it.

iTunes is supposed to be offering an upgrade in the next hour as part of the launch of Apple music. It is possible the pending upgrade is preventing your iTunes from working.

I very much doubt the upgrade files on a remote server are preventing iTunes from working on the computer. I haven't upgraded iTunes since 2007 and nothing has ever stopped it from working. 🙂

I would, however, just wait another 2 seconds at this stage until the new version becomes available on Apple's site and try that (unless you think you are better off with iTunes 12).