Folder icon don't show thumbnails/images

Hi, I'm using Windows 8.1 x64.

In the MUSIC folder I have 1 folder for each artist. In each Artist folder I have 1 folder for each Album. And in each Album folder I have all the songs, with the cover art embedded in them, in every single .mp3 I have.

In folder options I've set folders to show thumbnails, not icon. So, each Album folder's icon is the album art of the .mp3 files it has inside. BUT in the MUSIC folder, all the Artist folders don't show the album arts they have inside. Their icon is not a folder's icon neither, it's like thumbnails of folders:


And I'd like them to show the thumbnails of the albums they have inside. Well, the maximum amount of images that a folder icon can show is 2, so if I have more than 1 album in an Artist folder, then the icon should be 2 random thumbnails (of 2 albums).

An example here:

I put a song (with embedded cover art) in the desktop. The archive's icon is the cover art.

Now I create a NEW FOLDER (the icon is a default folder icon) called "Album". I put there the .mp3 file. Now, the "Album" folder's icon is the cover art of the .mp3 file.

Then I create ANOTHER new folder called "Artist" (default folder icon), and I put there the "Album" folder. And here, the "Artist" folder's icon is NOT the cover art, but the icon of the image above, and I want it to show the cover art.

Notice that all album's folders have only .mp3 files, not hidden images like "folder.jpg" or anything else, just .mp3 files.

What drives me crazy is that like a week ago, Artist folders were showing cover arts of the albums they had inside (they picked up 2 random images, cause folders can show up to 2 thumbnails).

Hi there?

How can I do this, that a "Mother" folder's icon shows cover arts embedded in the "Son" folder's icon?

-Folder A (rare folder's icon, image in the first post) contains:
--Folder B (folder's icon is the cover art of the files it has) contains:
---mp3 files with embedded cover art

I want A folder's icon to be the same as B's.