Need more info. Which player, which company, what type of batt etc, but im gonna try making a few assumptions.

Im guessing the battery in your player is charged by the USB port when the player is connected. If that's the case, you will need to first charge the player by leaving the comp turned on and the player connected for atleast 10 hours.

If the player is not charged by the USB port, the battery in the player is probably dead. Replace the battery.

its is a 256 mp3 player and the battery im usin is a uniross green battery i dont no about the chargin the mp3 player wuld do ne gd but i dont know if i can lol