How Do I Sync My iPod Again?

My computer recently broke down and deleted all my info. I had to re-setup iTunes but not re-install it. When I go onto iTunes now there is no music or video or anything except some sample album. I plugged my iPod in with the apple USB cord but its not syncing, and the sync iPod button under the file tab isnt highlighted so it wont let me sync. Do I have to erase all my content before iTunes will let me sync my iPod? I have no problem doing this but I have 3 purchased movies from the iTunes store that I dont want to lose. How do I get it to sync?