You can re-download app and ibooks for free, and if you are in the US you can also re-download music and TV shows, as long as they are still available in the store and you use the same iTunes account as you originally used to buy/download them : http://support.apple.com/kb/HT2519 . If you are not in the US then have you not got backups on, for example, external drives and or CDs/DVDs that you can copy onto the the computer and add into iTunes ? Have you double-checked that all the files didn't copy over by searching for them by name via windows explorer ?