It says.
Warning: opendir(uploads\admin_uploads\upload_sounds\mymp3): failed to open dir: No such file or directory in C: ...
So I think the problem is in the path you gave.
Try one of these.
$dir = dir('.\uploads\admin_uploads\upload_sounds');
, $dir = dir('\Myproject\index\uploads\admin_uploads\upload_sounds');
, $dir = dir('..\uploads\admin_uploads\upload_sounds');
I think its because your path is pointing to base and you should try relative path or true and correct absolute path.