Brewology

i have the samsung yp k5 and its the one with the built in speakers really cool.i got it from a friend and i also have the usb.the problem is i cant put my own music in...when i plug it in it cant find my samsung and all it does is charges i need some help finding it on my computer and i look at my computer and its not there also.fast help would be nice since i dont want to listen to the kind of music on the samsung...thnx