why wont my cds upload onto i-tunes?

I recently had to replace my harddrive and lost my entire i-tunes library ⚠ I am now trying to upload my cd collection back onto my new hard drive but most of my cds i try to load just eject themselves without even being recognised by itunes. Some do still load but even then they can take a long time. Any ideas what the problem might be? I now have Leopard. Many thanks