Why does Itunes not play my music library?

I have my Itunes library on my PC- fine, no problems. I can sync my Iphone(4), and play any music I want. My PC is an older model, running Vista. Just bought a new laptop running Win8. Sync Iphone no problems, but can't play any music from my phone, and the music does not show up in my Itunes library. What to do? I would like to make the laptop my primary computer with the phone.