Where did my itunes music go?

For some reason all my music in my itunes library deleted, so when I reopened it, it prompted me to set itunes as the default music player. However, it doesn't have any of the old playlists I sync with my iphone… How do I get it back to normal? Apple is *** useless

This question isn't very helpful. Were these iTunes purchases? Just download them again. If these were not bought in iTunes they might still be on your computer even if they're not on iTunes. Just import them again.