Q: Songs stored on an external drive & it crashed

Well if everything was on the external drive then everything was lost unless you had a backup made.  You may be able to restore items you purchased from the iTunes Store by redownloading, but not everything will be available, and of course you will have to rebuild your library, ratings, and playlists from scratch.  Anything else you will have to get from the source you used originally.

Downloading (using iOS or computer) past purchases from the App Store, iBookstore, and iTunes Store - http://support.apple.com/kb/ht2519 - enabled with iTunes 10.3 and newer; not all media formats are available in all countries (see: iTunes in the Cloud, iTunes Match, and iTunes Radio availability by country - http://support.apple.com/kb/HT5085); apps, books (not audiobooks), music, t.v. shows, and movies (some - not all studios have permitted this).  Downloading previously purchased movies and TV shows requires iTunes 10.6 or later.  Discontinued items not available. For items not included in the iCloud list (e.g., ringtones, audiobooks), or locations or computer systems where iCloud is not (yet?) available, you only get one download per fee paid.  Apple recommends,  "You always back up your iTunes library in the event that a purchased item is no longer available on the iTunes Store," (http://support.apple.com/kb/ht2519).

Additional tip at https://discussions.apple.com/message/24176756

  Select the iTunes Store on the left side of iTunes if you have the sidebar displayed, or with the button at the top right.
  Click on Purchased on the right side under Quick Links.
  You can re-download your available previous purchases.