There are two reasons for this. Firstly, it is possible that the WakaWaka Power+ does not contain enough energy to charge your device. Therefore the blue light turns off. You can check this by checking the status of the green lights on top of the Wakawaka Power+. If only one green light is burning, you first have to recharge the WakaWaka Power in order to charge your device again. Bear in mind that when charging the WakaWaka Power+ via a micro-USB charger, the blue light next to the USB port should lit.