Answer by SPRBRN for iTunes personal music library is empty

See If you don't see your content after you update iTunes

1. Quit iTunes.
2. Go to the iTunes folder that contains the iTunes library files:
3. Mac: From the menu bar at the top of your computer screen, choose Go > Home. Open the Music folder, then open the iTunes folder.
4. Windows: Navigate to \Users\username\Music\iTunes.
5. Drag the iTunes Library.itl file to your Desktop.
6. In the iTunes folder, open the Previous iTunes Libraries folder.
7. Find the file named iTunes Library YYYY-MM-DD where YYYY-MM-DD is the date you updated iTunes (Year-Month-Day).
8. Copy this file to the iTunes folder (the enclosing folder).
9. Rename the copied file iTunes Library.
10. Open iTunes.