How do I recover previously purchased music and apps?

On the computer, using iTunes, go to the iTunes Store main screen. Make sure you are logged in using the Apple ID previously used to make the purchases. Over to the right, under QUICK LINKS, find and click on Purchased. On the Purchased screen, select the media category, then find the previously purchased item(s). Click the button (with cloud symbol) to the right of the item name to download it.

NOTE: There is a Not on This Computer filter on that screen that may be helpful.

Sorry, what do you do if that doesn't work (including Not on This Computer)?

You need to be logged into iTunes using the same Apple ID (iTunes Store account) you used when you oiginally purchased the songs from the iTunes Store. You can check the Apple ID used to purchase a particular song by doing a Get Info on the song and looking for Account Name on the Summary tab of the Info window.

If you are still having problems, you should contact iTunes Store support, starting at this link

http://www.apple.com/support/itunes/contact/