Cannot sync videos onto my ipod

Hello,
I got my ipod nano 8gb 4th generation about a month ago. I put songs on it fine and then i downloaded some videos and when i plugged in my ipod and tried to sync them a message came up saying "itunes has encountered an error and needs to close." i kept trying but then that message started coming up as soon as i plugged in my ipod. heaps of different problems have been happeneing and now i can't even play any songs on my ipod:(.