this deals with my windows media player.  my computer is a dell inspiron 1501 with windows xp.

i have lots of music files.  some are from cd's, some from limewire, some from youtube.  i get the you tube files by using a program called  listentoyoutube.com
it somehow copies audio from a youtube file and stores it in my comp.  

all my music is in a single place on my comp.

sometimes, i go to those tunes, highlight several of them, and then click "open with windows media player".  they appear on the players, and i turn them into a playlist.

i play the  list several times over days.  

suddenly, for no apparent reason, tiny blue icons with the small letter "i" in a circle--as in "information"--will appear next to certain songs.  the message says, "windows cannot find file".  

i go to the place on my comp where these are stored, and they are there.  i can open them.  i can play them with WMP.  i also can again copy them as i described above, make my playlist, and enjoy it.........for a while.

but always, after a short time, they again disappear. not everything on the playlist, just these certain songs.  

how can i fix this?

thank you very much.