The battery of your Player may be empty; recharge the player by connecting it to your computer
You may not have held the Power On/Off button long enough. Press and hold the Power On/Off button until the display turns on (approx. more than 1 second)
If nothing works, try doing a soft reset by inserting a small pin or other sharp object into the reset hole located on the side of the player. Hold until the player shuts down
(Note that your songs and data will not be lost or corrupted by a soft reset)