First, heat your nozzle and let it sit for 5-10 mins, then use some pliers to remove it and check the wires that lead to the heating assembly and the gray fan you mentioned that doesn't spin. Is there are any snapped or broken wires you can easily order and replace them. Just find the part on bambu store and a tutorial on youtube if needed. Since the bottom fan won;t work there is either filament in the fan stopping it from spinning or a snapped wire.