Hey cantcontinue,
Welcome to Apple Support Communities. The information below may help.
If you still have the Windows 10 computer, you can transfer your iTunes library from it to the new one by following the steps here: Move your iTunes library to another computer.
Here's another article that may help with restoring your iTunes library to the new computer: Back up and restore your iTunes library on your PC.
If you're missing iTunes purchases, follow the steps below to download them.
1. In the iTunes app
on your PC, choose Music from the pop-up menu at the top left, then click Store.
2. 
3. Click Purchased (below Quick Links) near the top right of the iTunes Store window.
4. Click Music, Movies, TV Shows, or Audiobooks near the top right of the Purchased page.
5. Purchases available for download are displayed. You can view all of your past purchases, or just the ones not currently in your iTunes library. Items already in your library aren’t available for download.
6. If you select Music, you can view your purchases by song, artist, or album. If you view by album, click an album to see which songs are available to download.
7. To search for an item, type its name or a keyword in the search field, then press Enter.
8. To download an item, click its iCloud Download button
.
For future reference, the steps are also located in this article: Download previous iTunes purchases on PC.
If you have an Apple Music subscription, enabling Sync Library will allow you to access your library across all your devices which would include the Windows PC. For information on enabling Sync Library on your Windows PC, review this link: Use Sync Library to access your music library across your devices.
Take care.