Songs on Itunes appearing grey and unable to select one?

I uploaded my Ipod nano onto my Itunes and now I can't edit the music on it. I signed in, and I also authorized the computer. I see the list of songs that my ipod has in my Itunes, but it appears grey and I am unable to play the music or add music. How do I fix it? I'd like to add music to my Itunes and play my music on my laptop.