iTunes 12.2 black full-screen on launch
I had a problem after upgrading to iTunes v12.2 (12.2.0.145) on a fresh upgrade to Yosemite 10.10.4. I've fixed it myself and I'm posting this because I didn't see any other questions with this exact trouble. Maybe this post will help someone else.
The last time I used iTunes before the overnight update, the app was in full screen mode. This morning, the desktop assigned to iTunes was completely black and none of the keyboard shortcuts would work to return to a windowed app screen. In fact, after following another suggestion, I was able to get the "iCloud session has timed out" prompt, but the password field was unresponsive to keyboard input. Only a Force Quit would close the application. Strangely enough, using the Space bar to start playback did work, but the screen would remain black. Also, launching a movie or music file from the Finder would launch iTunes and begin playback, but the app would still retain the completely black full screen.
Here's what I did:
Launch iTunes while holding the Option key to force the app to prompt for a new Library location. From this prompt, create a new, empty library anywhere on your hard drive. iTunes will now launch normally. Make sure the app is not in full screen mode and then Quit the app. Holding the Option key, again launch the app and this time Choose your previous, full iTunes Library. It should launch normally into a non-full screen window and function normally. If you prefer full screen mode, you can now use that option and everything should function as normal.
I hope this helps!
iMac, OS X Yosemite (10.10.1), 27" iMac Core i7 Quad 12GB