This may not be the solution to your problem, but it's something to check before you start making changes to your system: Is it possible that those particular music files really don't exist any more on your system? In other words, could you have downloaded only a shortcut to a link that is no longer in existance? I have had this happen a number of times when I believed I was downloading music, only to find out that what I "downloaded" was only a shortcut to the site that was hosting that particular piece of music. So eventually, if the original site no longer had that piece of music available, the result was that my shortcut link was no longer good.
One of the ways you can check to see if that applies to any of your missing music files is, (assuming the system will still allow you to do this) to right-click on the file and go into Properties to check the size to see if it's the size you would expect of a full audio or video download --- or is it only the size you'd expect of a shortcut link.
If that's not the case, the next thing I would do is an Advanced Search for each of those files. By checking "Music" on top, you can limit your search to music files only, but be sure to search your entire system, not just the indexed locationss. And be sure to check the box that says: Include non-indexed, hidden, and system files.