mafmatik

if i try to rename a music file,a message appears saying "if you change a
file name extension,the file may become unusable".if i go ahead and rename
the file ,windows media player does the not recocognise the format and the
song can never be used again.i didn't have a problem renaming my files but
then i lent my laptop to my father and since it came back to me this is the
problem i'm having.i am sure he has just changed a setting but dont know what.