I have an iPad 2 16GB Wifi which I recently got a few days ago. Everything works fine, but I can't sync music and books to it. I add the music and books to iTunes, and made sure that the checkboxes for those were ticked. But when I sync it, none of the music or books are there in iBooks and iPod. The strange thing is that the space those take up show, but they still aren't there. What could be the cause of this and how do I fix it?