Will it still do it since I used to different computers to put music on it? I need to get a battery in the morning and try it.
Yes, it should. Your mp3 player doesn't care where the music came from. Once it's on the player, it's on the player.
If Windows Media player recogonizes your mp3 player (and it should), then you should be able to open up it's list of contents and delete them.