Maybe try reinstalling? I'm assuming you have a backup before you delete anything - just in case.
Download the installer…
Quit iTunes, delete the app, empty the trash & run the installer then reboot for what it's worth.
You could also try holding 'alt' as you open iTunes, you should get a dialog to select a music library. If you select a folder on your Desktop (create one first) & iTunes runs OK, you know the issue may be in your library. Quit & reopen iTunes holding alt to switch back to the old library.
You may also find information in the log files, open /Applications/Utilities/Console & look around for iTunes logs (probably in your account/Library/Logs) and look for iTunes crash reports. It may give you an indication where to look next. If you get a dialog asking to submit the report, do so. It may mean the issue gets looked into.
Another test is to create a temporary user account (in System Preferences) & try iTunes in that account, it may indicate the fault is either in your iTunes library, or the iTunes preferences files.
It may also be worth opening Disk Utility (in the Utilities folder) & running the repair permissions on the boot disk.
Repairing permissions rarely fixes anything, but it's worth a try.
I'm not sure you issue is related to the original question, there is no mention of Airplay, so it may be different.
You should reboot everything, whatever you are 'Airplaying' to, your wifi router (if you can reboot it) & the Mac.
Then check your system prefs for the sound output device, see if selecting a different one makes any difference.
Have you installed any other software that causes your Mac to become an Airplay reciever (like AirServer), it may conflict so quit it or uninstall?
Try opening iTunes in another user account - if that works you know you need to look at your own account.
You could also try a safe boot, which will disable certain third party & certain Apple extensions…
Bear in mind networking may not work & the OS features will be limited until you reboot & leave the safe boot, you may need a wired keyboard & mouse too.
Look for the logs to see if they contain any error message that can be searched for in Google (remove the date & time & process id [numbers in brackets] from the text if you google it).
You can also watch the 'All messages' or 'Console messages' items in the logs within Console.app. Keep an eye on those for new entries being generated as iTunes keels over.
Log output may be gibberish, but it may give you something to go on.
Reverting might be for the best, I suspect Apple may slowly add some features back to iTunes like they did when the trouble hit the fan with Final Cut Pro X or Lions iCal stitching.
They have a cycle of taking a few years to make something really good before burning it down & starting over (or abandon it altogether).
I had the same problem when I upgraded to iTunes 11. I had to leave my computer for a bit an left iTunes open. When I came back, it was working fine and had gathered all my icloud music files and showed them along with the cd's i had burned. My pc is old as pc's go and I'm going for a new iMac very soon so my slow pc may have been the problem.