The computer I originally started using iTunes on a few years ago is no longer functional. How do I make the same library appear on my new computer with the newest iTunes?

The computer I originally started using iTunes on a few years ago is no longer usable, but for some reason some of the songs I have now are not showing up in my library on the new laptop I just bought. How do I consolidate the total songs on my iPhone to include them all in a new library on my iTunes in this new laptop? And why isn't this new laptop letting me update to ios 6 without deleting everything on my phone?