In such scenarios normally a soft reset makes the player reset. Try to reset it by applying pressure in the small hole for reset.The main reason is improperly disconnecting the device from a USB port. This can cause the firmware to be corrupted. The solution is to allow the battery to completely drain, then before connecting to any power source, press the play button for 30 seconds. This resets the firmware. How to properly disconnect from a USB port is on page 17 of the manual and applies to any device
Let me know if there is anything else to clarify.