iPod Little check boxes by songs have become unchecked

[Yodalogger]

I recently opened my iTunes library to find that almost all of my 2500+ songs were unchecked. I've tried using the cmd+click on one of them to get all of them to click, but it causes iTunes to hang. Any suggestions on 1) how this may have happened 2) how to "fix" this short of clicking 2500+ individual tiny little check boxes? Thanks

 

[Cynicalone]

So can you do the Command "A" to select all the music then right click and select "Check Selection"? Or maybe break it up in groups of 500 songs at a time to keep iTunes from hanging.

As for how it happened I don't know. So many different possibilities.