I have been using iTunes for more than 1 year now, and one of the problem I have seen many times is that if I had added the songs added to the iTunes music library and for some reason the song gets moved it will say cannot found that song and cannot play, but still you can relocate the song in some other folder in that case or just copy the song in the same folder where the iTunes is searching for it.
iTunes allows you to locate the song, by telling you the folder where it is searching for that song. Below is how you can find the song folder of a song track added in iTunes music library.
Just right click on any sound track in iTunes music library and select the option to show in windows explorer as shown in the image below.
This is how you can find a song folder location and then fix the problem by copying the same sound track with the same file name in that folder to fix the problem of could not locate song in iTunes when you try to play it.