Here's the solution for Windows computers and possibly Apple computers too, (I know there is a version of CCleaner for mac, but I don't own a mac so I cannot guarantee that this will fix it -- though it is likely that it will -- so it won't hurt to try)
EDIT: WINDOWS ONLY! Sorry about that.
Before doing anything, please backup these folders and files from your iTunes folder: Album Artwork, iTunes Media, iTunes Library (iTunes Database File), and iTunes Music Library (XML Document). Next, uninstall iTunes.
Now go ahead and download Piriform's CCleaner at filehippo or any other preferred website (
www.piriform.com is a wise choice as it has a version for those using a mac). Once installed, open CCleaner and click on "Registry" (just below "Cleaner") then click "Scan for Issues". A whole list of issues/errors should appear with a check to the left of each one.
At the very top of this list of issues there will be the words "Problems" , "Data", and "Registry Key", as well as a check mark to the left of the word "Problem" -- uncheck it and all the check marks should disappear.
Now you need to search for everything that has something to do with itunes. You can do this by searching through the Data column. After checking these items, select "fix selected issues". You may need to go through this process a few times before all traces are deleted.
Once you have finished you can then proceed with reinstalling itunes.
iTunes should work fine now. All you have to do is transfer the backup files back into your iTunes folder.