entire iTunes library gone

Soundwave, here's one way to recover your library.

1. Quit iTunes.

2. In the folder [username] > Music > iTunes, locate the file called iTunes Library.itl and drag it to the desktop. If you find a file called either iTunes Library.xml or iTunes Music Library.xml, drag that to the desktop as well.

3. In the folder Previous iTunes Libraries, choose the file with the most recent date written into the file name. (It will look something like: iTunes Library 2015-17-01.itl) Make a copy of this (File > Duplicate) and rename the copy to iTunes Library.itl

4. Drag this file into the Music > iTunes folder.

5. If your media files are stored on an external drive, make sure that drive is mounted on your computer. (It should appear on the desktop or in the sidebar of a Finder window.)

6. Open iTunes.

Now you should be seeing your library as it looked before the tracks were lost.

There may be songs and playlists missing, if you added them between the time of the backup and today. If you have trouble remembering or finding them, there's an AppleScript utility for locating all the files in your media folder that are *not* listed in your iTunes library: http://dougscripts.com/itunes/scripts/ss.php?sp=musicfolderfilesnotadded2

If you use Time Machine, you may be able to find a more recent version of iTunes Library.itl -- a backup made just prior to updating iTunes. In this case, instead of following steps 3 and 4 above, you can select this file and restore it to the Music > iTunes folder.

I hope this helps sort things out.