I have a problem which I assume is related to others described above. I have just got a new iMac, with OS X 10.10.4. I have iTunes 12.2.1, which I think was upgraded on to my old Mac on 16 July 2015. (That's the date on which it was last modified.) I was previously using an old (pre-2009) MacPro, with OS X 10.7.5. I transferred everything from my old Mac to the iMac from a back-up, as a direct connection between the two didn't work.
When I open iTunes by clicking on it, it shows a menu list in the menu bar (iTunes, File, Edit, View, Controls etc.) but virtually all the options under each of these heads are greyed out. (The only exceptions are "Quit iTunes", under iTunes, and "Start Dictation…" and "Emoji & Symbols" under Edit. All items in the Help menu are OK, though.)
If I click on a piece of music in my Music>iTunes>iTunes media>Music folder, the result is the same - i.e. with virtually everything greyed out. (This opens iTunes, if it wasn't already open.) That music plays. Then silence.
I tried opening iTunes while holding the Option key, as suggested in one of the postings above. iTunes apparently opened … but the result was getting nothing in the menu bar at all, except "iTunes", and even that had no options below it - not even greyed out. Clicking on a piece of music did not make it play. The only way to quit iTunes was to Force Quit it.
I tried creating a new ITunes Library.itl file, as suggested by Apple in its "If you don't see your content after updating iTunes" advice. This made no difference.
Other suggested solutions would be welcome!
P.S.: I just looked at the iTunes.app info, by clicking on Get Info in Finder. I saw an option to "Open in 32-bit mode". I tried that, to see if it made any difference. It did. When I opened iTunes with this checked, I got the same result as I got by clicking on a music file. That is, nothing in the menu bar except "iTunes" with no options below it. So I've unchecked it again.
Are the Sharing & Permissions privileges relevant? I have not tried to change them.