What exactly happens when you try to sync?
Was the iPod previous synced to another iTunes library/computer?
Have you successfully synced from this iTunes library/computer before?
If so have you done anything like update iTunes on the computer since it last successfully synced?
Do the songs play in iTunes?
Does any media now sync to the iPod?
Do you have the right boxes checked to sync?
Try syncing using the manual method
Do you have any Restrictions (Settings>General>Restrictions) set that would prevent syncing those songs? (iTunes purchases only)