All of my kids have experienced problems at one time or another, when upgrading iTunes on their laptops. The version number doesn't matter, as this has happened for the last couple of years, so the version number has changed. It isn't consistent. What is consistent is sometimes, but not always, after upgrading iTunes, it will have lost all of it's information about the music, podcasts, etc, that it had. And yet if I bring up Windows Explorer, I can find all of it there. It's a pain to have to recover that.

The pertinent question is, how do you recover all of the music, podcasts, playlists, etc, that is on the computer, but iTunes doesn't show it in the library?

Second, what causes iTunes to do this in the first place?