Hey Edwin_Kirika!
I’ve been there! It sounds like you’re running Mac OS Catalina? Does it give any particular error message?
Also, did this happen after any particular event? (Such as an update/transfer/etc.)?
I’m thinking a few solutions, but it may depend on those answers, if you have the time just let me know! (Most likely the library needs to be rebuilt, which can be a quick solution, depending on the amount of music you have)!
One way to test the issue is to create a new Music/iTunes Library:
Use multiple libraries in Music Mac:
https://support.apple.com/guide/music/use-multiple-libraries-mus7663a920a/mac
But first:
If you open Finder > Go > Home > Music:
Do you have a Music folder in there? Or an iTunes folder? Or both?
I’m just wondering if your iTunes Media/Music was either transferred onto this Mac from another older one, or, even if you store your music on an external hard drive to save space, etc.
Another useful piece of information may be where the media folder is located:
If you open Music/(Used to be iTunes)/ Preferences/Files, from the top menu, you will see the path to the music the app is looking to, is this the actual location where it is supposed to be?
Likewise, can you confirm if you are subscribed to Apple Music/iTunes Match or not? And see what it shows in Music/Preferences/General? (As far as “Sync Music”?
Cheers, just let me know happy to help if I can.