I can not download any of my previously purchased tones

Ringtones (and audiobooks) are currently a one-time only download from the store. If you don't have them on your phone, nor in the Tones part of your computer's iTunes library or on a backup, then if they are still in the store you can try contacting iTunes support and see if they will grant you a re-download : http://www.apple.com/support/itunes/contact/ - click on Contact iTunes Store Support on the right-hand side of the page