Transferring songs to a new iTunes

Hello,

I have an iPod Nano. I originally used it with iTunes on my PC but no longer have access to that PC so have downloaded iTunes on my Laptop. How do now transfer all of my music from my iPod to new iTunes?

I have authorised my new iTunes and followed the "Transfer Purchases" options. This has worked for some songs but there are 100 that it hasn't transferred and keeps saying that I am not authorised to play them on this computer. It goes on to say about authorising this computer which I have done? Any ideas how I get the remainder of the songs to transfer to my iTunes library.

Also, is it possible to transfer the songs that I uploaded via CD as opposed to purchased?

Thanks.