My iPod touch won't sync, what should i do?

Okay so heres my problem. I have downloaded new songs onto my itunes, but the sync button is gray and won't let me sync my ipod ... when i charge my ipod it says it is charging but never says it is syncing .... and the picture that usually comes up on the side of my itunes isn't coming up anymore. what should i do?? how can i get my itunes back to normal??