Playlist issues

I figured out how to create playlists and have been successful, but one day I go to playlist and the music is replaced with another playlist. When I look at it while connected to computer the music is correct. Someone help me figure out what is happening. I am so frustrated.

Could you please give more information so that we can help you?

I have my music organized into the Music folders and within the folders I create a playlist. I think this is the way to do it since it seems to work ok. PLease advise if that is wrong. The problem is that a folder that contained the music and playlist it should have suddenly has the music and playlist from another folder in it for no apparent reason.  I hope this clarifies my original question sufficiently.