The iTunes application in your new computer has not yet mapped its library (database) to your NAS drive (location). Try File/Add Folder to Library... and navigate to the folder in your NAS where all the music files reside.
When the mapping process is complete, go back to Edit/Preferences/Advanced/iTunes Music Folder Location > Change...and once again navigate to the same folder in your NAS (assuming it's the same folder you wish to add music files in the future).
Hope this helps.
When the mapping process is complete, go back to Edit/Preferences/Advanced/iTunes Music Folder Location > Change...and once again navigate to the same folder in your NAS (assuming it's the same folder you wish to add music files in the future).
Hope this helps.