Currently Being ModeratedJan 4, 2013 7:22 AM (in response to eicher.a)
Contacting the iTunes Store - http://www.apple.com/support/itunes/contact/. At the bottom left, you will see a "contact support" link. Just select it, then select "iTunes Store", and the select "purchases, Billing and Redemption". Follow the on screen instructions.
They will recommend in the future, you back up your data, but usually grant a one time "re-grant" of all your purchases.
Currently Being ModeratedJan 4, 2013 8:42 PM (in response to eicher.a)
You don't need to contact anyone to redownload music. Everyone can redownload as many times as they want.
You cannot redownload audiobooks
Failing to maintain a backup is a big mistake. Please backup your computer.