Why is my iTunes freezing when I sync my iPod touch/iPhone, and how do I fix it?

My iTunes account has been freezing every time I try to sync my 4th generation iPod touch or iPhone 4 lately, and I have to restart my computer to do anything. It typically freezes while transferring purchases, but sometimes will continue to the start of syncing music and just not progress. Because they won't sync, I have music on neither my iPhone nor my iPod. My iTunes, iPhone and iPod are all up to date, all fully charged when I try. I don't have any new software, I have tried factory restoring, I have tried defragging my computer, restarting each device, alternating between the iPhone and iPod, all to no avail. Does anyone have further suggestions?

I can't help you, but I'm trying to figure out the same thing. D: Mine is exactly like yours, won't sync, iTunes freezes, won't restore. I've restarted my computer and everything._. I have a fourth generation nano too. It asks for a disk check but it never works, not that I know what that means. But if you figure it out, it'd help me too. :/ Sorry if I wasted your time.