I think there is something that has disabled your back up feature and it has nothing to do with itunes, anyway. there is something called "itunes backup disabler" once you download it you'll have two options
1. enable backup
2. disable backup
once you get it, click on enable and hope this will help you.
More reviews: How to transfer iPod/iPhone/iPad to computer or iTunes
It includes the transferring of music, photos, videos, SMS, Contact ect. between iPod/iPhone/iPad and computer(PC or Mac).