Q: External Hard Drive Crash

It depends upon what country that you are in (music can't be redownloaded in all countries), and whether the tracks are still in the store (record companies occasionally remove them). What you can re-download will show via the Purchased link under Quicklinks on the right-hand side of the iTunes store home page on your computer's iTunes. If a track shows as 'downloaded' under that link, as opposed to have the cloud symbol against it for redownloading, then you probably still have it listed in the Music section of your library (where you would click on it to play it) - deleting it from there should then give you a cloud symbol against it