What is the problem with my iTunes?

Whenever I plug my iPod into my computer the iPod is recognized, but when I go the delete songs off the iPod the whole music list is in a pale shade of gray and it doesn't give the the option to delete them. Also,when I try to add new songs to the iPod a waring symbol (red circle with a line through it) comes up over the song as I am dragging it to my iPod. The computer says that it is authorized, so what is the problem?