Q: my computer crashed and had to be restored and now my purchased audio books and movies and some songs are missing

Audiobooks are a one-time only download from the store, and what else you can redownload depends upon what country that you are in and whether they remain in your country's store (content providers occasionally remove their items). You can copy them back from the backup of your downloads that you've been keeping and add them via File > Add To Library to your iTunes library. If you haven't been keeping a backup, then for those items that are still in your country's you can try contacting iTunes Support and see if they will grant a redownload : http://www.apple.com/support/itunes/contact/