HT203167 Music files present but iTunes can't see them

Question

OK, I have the unfortunate situation that all of my music files appear to be present and correct, but iTunes just shows nothing at all. I have tried all of the suggestions I can find online, including changing the Music folder using iTunes Preferences/Advanced, selecting a new folder on startup by pressing the Alt key on my MacBook, and re-installing iTunes from scratch, but nothing seems to work.
Config: OS X 10.7.4 (Lion) and iTunes 10.6.3 (25)
I have a sneaking suspicion that this occurred just after the system upgraded my version of iTunes, but can't be 100% certain since upgrades seem to happen all the time.
This is obviously frustrating, so any advice would be gratefully received. It's an unusual case I think, in that I've got my music and backups, but can't actually play the blasted stuff with iTunes. As a last resort I may have to just re-import it all, but this will take and age and will almost certainly lose my playlists, so I consider this a last resort. Everything is there on the 'puter, so I don't see why it has to be so **** difficult!

Answer 1

Oh well, nobody replied so I went out on a limb and thought I'd try a combination of the various fixes that I had seen for similar problems on this forum. This seems to have worked, so I thought I'd document them here, in case anybody has the same problem. Yes, I know it's just repeating stuff that other people have said (by definition), but it'll be useful for me, even if nobody else ever uses it.
I'd pretty much resigned myself to screwing everything up, so I thought I might as well tidy up my iTunes folders to begin with, since these had got rather scrambled over the lifetime of iTunes.
As a first step, I exitted iTunes and used the OS X Activity Monitor to kill the iTunes helper.
I then moved all of the various iTunes media folders from the "iTunes" directory to the newer "iTunes\iTunes Media" folder. The media folders that I had on my system were: Album Artwork, Audiobooks, Books, Mobile Applications, Movies, Music, Podcasts, Ringtones, TV Shows, Voice Memos, iPod Games and iTunes U. Note that this is just what I found on my setup - ymmv.
Rather pleasingly, by performing this step I located a number of orphan media files that I hadn't seen for ages (years in some cases), so it was a step well worth doing imho.
Since I didn't want to waste time actually moving any files at this stage, I started up iTunes and set the iTunes/Preferences/Advanced dialog to disable the "Copy files to media folder" option.
I then dragged each of the media folders from the Finder into iTunes. I was really pleased that it was able to automagically assign them to the correct categories under the iTunes LIBRARY. Apart from the music selection the transfer was pretty fast, which made it easier to stomach. I also began by transferring some of the smaller folders (e.g. Books) which reassured me that the process was working correctly.
Note that the "File/Add to Library..." menu option did not work in the same way - only dragging from Finder.
After all of this, my media content inside iTunes was pretty much pristine, with all of the media located, in the correct place and with al of the artwork as expected.
Unfortunately, I had lost all of my playlists, which is something I had resigned myself to. However, I'd read elsewhere that these might be recoverable from the "iTunes Music Library.xml" file. I did a quick scan of this file and was able to locate some of my old playlists - much to my surprise (recall, this was after I had already made several attempts to recover my files, so I was expecting this to have been scrambled).
I therefore copied this file to my desktop and used the iTunes "File/Library/Import Playlist..." to see if I could recover any playlists from this file. Amazingly, they all re-appeared. Better yet, they actualy worked, despite the fact that I had moved loads of the files during the earlier housekeeping stage. A few playlists were duplicated but it was a trivial step to delete the unwanted ones.
To finish up, I re-enabled the "Copy files to media folder" - fully expecting this to take an age to move the files around. Once again, I was pleasantly surprised that nothing seemed to happen - possibly because all of the media files were already in the 'correct' location - I'm not sure on this point.
So, to finish - all of my media files are back in iTunes, all of the playlists recovered, and I've also recovered some music files and movies that I thought I'd lost. Not a bad outcome for a couple of hours work (most of which was during the initial housekeepign step).
If I had the time, it'd be nice to write a script to do the housekeeping step, but well, you know how life goes...