My bet is that both iTunes and WMP (windows media player) is set to discover, add, and arrange music. No duplicate tool I've seen is perfect so how to avoid deleting your last copy is probably the challenge.
Turn off the automatic add and arrange in both then be sure your files are safe before you look and try any duplicate remover. That way you are ready for the worst.
Between windows media player and my ITunes they seem to be copying each other. I open my music library in windows and any album will have every song 3 to 5 times. I keep a terabyte external drive hooked up at all time for back up etc. but it is getting full and I haven't added anything in quite some time. I don't know why this is happening and or what I have done. I assume its me as not very tech savvy. So also will need a recommendation for a good duplicate remover. Thanks Randell