Did you try holding down the power button for at least 30 seconds, then try to restart the player again?
Did you insert or remove a card while the player was on? A card should only be inserted or removed when the
player is off. What format were the songs that you put on the player? If there is a card in the player, is it class 4 or slower? Sandisk players often have issues with cards faster than class 4. If there is a card in the player, did you try turning the player off, removing the card, then restarting the player?
Did you try manually reloading the latest firmware?