Thank you for participating in the Apple Support Communities.
Congratulations on your new computer! I know I'd want to have all of my content on a new device, so let's see what we can do to troubleshoot iTunes.
There are a few possibilities for why your content isn't appearing in iTunes. These articles are a good starting point for checking the features and settings in iTunes that might cause your content to be hidden.
If you haven't already, use the steps in this link to try downloading your purchases again:
Redownload apps, music, movies, TV shows, and books from the iTunes Store, iBooks Store, and App Store - Apple Support
If you don't see your purchases, it's possible that they're hidden in iTunes. This link will help you unhide them:
Hide and unhide music, movies, TV shows, audiobooks, and books - Apple Support
For your music, if you're using iCloud Music Library, it's possible you need to enable this feature on your new computer:
Turn on iCloud Music Library - Apple Support
Take a look at the steps in these articles. If your movies and music still don't appear, please let us know and we can investigate further.