There could be several reasons, all of which are designed as either safety precautions or to save battery charge:

• If the device is activated for longer than 5 seconds, the ePod will automatically shut down.
• Your ePod battery has run out of charge so you need to place it on charge.
• It may be time to change your ePod cartridge.
• There may be dirt accumulating that may affect connectivity between the device and the cartridge. You can remove dirt with a dry cloth.