I just got a kangertech kbox mini from a friend who wasn't using it and it worked fine after the first day and then started making weird bubbling noises and not firing whatsoever!! i changed the coil from a 0.5 to a 0.15 and reassembled it many times but there's no change. the screen doesn't specify any problems and i've tried different wattage but it's continuing to not work!! pls help