5th gen iPod will not sync

[DH78]

I'll try to be specific...

I got my 30 GB iPod 2 years ago, which I think makes it 5th gen. I have it formatted and managed with my MacBook. I often plug the iPod into the PC I use at work, simply to charge the battery. I always select "Don't reformat" when asked by the PC.

I think that I may have accidentally chosen "yes" the other day, because my iPod was completely empty. I restored with my Mac, and have now been trying to sync with iTunes. It gets about 150 songs into the sync, and then the iPod starts whirring. I then get an error message saying my device was ejected improperly.

Help! How can I sync up my iPod to iTunes?