My continued fix for such was a backup copy of iTunes. You say it's 50GB so let's look up the price of a 64GB memory stick as a second copy of that.
http://www.amazon.com/SanDisk-Ultra-Low-Profile-Flash-SDCZ43-064G-G46/dp/B00LLEODCK/ shows up as about 20 bucks.
No one I know edits XML files for free today. This may upset those that lost content but this is how many figure out that backups are necessary. Some have called this unhelpful but such help so far has been costly. That is you hire a computer consultant and put them to work.
iTunes was working great holding 50 GB of teaching/music. But while I loaned my desktop, Windows 7 ultimate, to my friend while I was away, an automatic iTunes update or two or three occurred (I was gone for 6 months). Also while on loan my PC crashed and I was left with this problem. I have a backup, but with it iTunes can't find the actual music that goes with the playlists listed on the left pane. Here's the details:
I have a separate backups of several dates of the .itl and the .xml files, but no matter what version of iTunes I download, these data files show me only the playlists but don't tell iTunes where to find the music that matches them. My iTunes Music folder is 40 GB large. So, they are in there somewhere because I always copy the source file when I add them into iTunes.
Playlists are all there on the left but the music on the right is not placed under the right playlists. I think the iTunes version was 10.7 or 11.3 that last worked but now downloading those and using those saved .itl and .xml files won't fix this problem. I've tried every combo I can think of but no success. I'm missing 50 GB of great teaching and music!
I've searched to find someone who knows how to look into the XMl file to see what ver. of iTunes it matches with but so far no results. This is so frustrating.
I'm sure someone a lot smarter than me knows how to fix this---Pls help.
I've also tried several times to join the Apple iTunes forum but cannot get registered as a user. Sign up page keeps asking for info I've already typed in, so I can't post there.