Why can't I find music files in my Itunes folder?

It is counter-intuitive, but the "iTunes Media folder location" setting is not used by iTunes to locate the existing content of its library or, as is the case with some other applications, to specify a location where any media files are automatically added. That setting only determines where new additions to your library will be places (in conjunction with other settings). For music:

• Imports from CD, purchases from the iTunes Store, and files added to the Automatically Add to iTunes folder will always go into <iTunes Media Folder>\Music\<Artist>\<Album>
• Media added using File > Add File to Library or File > Add Folder to Library operations will be copied to that location if the "Copy files to iTunes Media folder ..." checkbox is selected.

It's not clear from your description whether your issue is:

• you have music files/folders in C:\users\myusername\Music\iTunes\iTunesMusic but these are not shown in the iTunes library, or
• the songs/albums are listed in the iTunes library, but can't be played because iTunes cannot find the media files.

Can you clarify?

Right-click a song and see if there’s an option to locate it. If not, search the computer for files with the MP3, MP4, M4A, or M4P extensions.

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