OK, first of all (assuming you on OSX10 +) make sure you're logged in as admin, navigate to the Application folder and right or option click iTunes.app and select "Get Info". Click the padlock, enter your password and change all the permissions to read and write. Close "Get Info" and simply delete the iTunes app.
Google iTunes 10.7 DMG and download it. Google and download Pacifist. It's shareware so when launched a timer will start and you'll have to wait a few seconds to use it, then a couple of pop ups will appear asking if you want to install some extras, choose to ignore them. Once Pacifist is open click the "Open Package" button and navigate to the iTunes DMG. In the window that appears click on the "Contents of Install iTunes.pkg" to highlight it. Then on the top left of the Pacifist window there is a downward arrow marked "Install". Click on that and let Pacifist run. Several pop ups will appear - choose to "Replace" to all.
When the installation has finished make sure iTunes is not open then navigate to your "Music/iTunes" folder. In that folder is a file named "iTunes Library.itl" - delete it. Then in the sub folder named "Previous iTunes Libraries" you'll see files with dates in the filename i.e. "iTunes Library 2012-12-05.itl". Copy and paste the one with the latest date to the main iTunes folder, where you deleted the previous .itl file, and rename it to remove the date.
Finally in the Apps/Utilities folder you'll find Disk Utility. Launch it and select the hard disk "Mac", then click the button "Repair Disk Permissions". This will take around 5 minutes or more (despite it saying it will take 2 minutes!!) and you'll see it repairing a lot of iTunes files but be patient it will finish. When done close Disk Utility and I'd suggest a reboot (although I didn't) and launch iTunes. You might need to sign in to your account again but maybe not and all should be good!!!
Good luck.