This Sounds Stupid =(

I have a suggestion as well...if the batteries have already been changed, look to see if the "hold" button is on. The same thing happened to me and I was freaking out.=P just check the batteries and the "hold" button, and hold the play button down. If this doesnt work, i have no idea.

On my Nextar mp3 it has a little button on the side-that's the button you hold to turn it on.

faulty power switch on the play button? Try reflashing the firmware most MP3 player companies will post firmware updates on their websites usually under "support" once you reflash the player try it again. If it still doesn't work i have one other idea although it may sound stupid. Did you put batteries in it or is it an internal battery?