To help us give you player-specific advice, you should tell us what brand you have. How did you transfer music - drag and drop through Windows Explorer or did you use software? If you used software, what did you use and what version is it? What kind of files are you trying to play? Are they mp3 files? Purchased, as in protected WMAs or AACs? When you say you can play it when connected to the USB port, do you mean that you're playing your songs through your computer's speakers?
My first thought is that it is defective and that you should exchange it. Since I have an iPod, I may not be able to help you, but someone else might.
Can you please tell me what is wrong with my mp3player....I recieved it for Christmas and downloaded songs onto it and put them into seperate folders. It will play when I put it into the USB drive on the computer , but it will not play otherwise. I have changed the battery and still, it wont work.
Thank you in advance,