hm... maybe you deleted a folder that your music was in and didn't realize it... or maybe you deleted a program that the files were linked to and didn't realize it. If your computer deleted your music files by itself... then... well... you might want to get that checked out... maybe my computer is well behaved, but it's never deleted anything that I didn't tell it to delete.

PS, I have uninstalled and deleted a version of Kazaa from my computer before... and with it went 1500+ songs... but I take the blame, I won't brush it off on my computer. haha