iPod Sync Problems.

Hello. I am having problems with my iPod Classic 120gb. It worked fine for a few months when I got it, which was December 08. Now it will not completely sync my library. Whenever I put anything on it, once it gets 2.23 or 2.24 gb filled up it stops syncing. I've tried everything. I called Apple and spoke with 2 different people about it, and they also sent me things through my email to try. Nothing worked. I also tried using it on a Windows Vista Ultimate OS and the same problem persists. I think I have a defective hard drive. Help is much appreciated. Thanks.