Problem with syncing from itunes to my ipod touch...please help!

So i have had my ipod touch for a little while and have been able to sync it with itunes perfectly fine...but this all changed the other day when i bought some new songs from itunes and one of the songs only partially downloaded. Ever since then i haven't been able to delete it or add any new songs onto my ipod because it will no longer sync. You click on sync and it looks like it is going though the motions...but then I check my ipod and nothing has changed.

How can i fix this....it's really frustrating and i'm not too sure how to get it to be able to sync again 😟

Does anyone have any ideas...it would be greatly appreciated! 🙂