The parts most likely to give the trouble that you experienced are 3, 4 and 5 - nozzle, O-ring and needle. It is very easy for dried paint to build up inside the nozzle and prevent the needle from seating properly, and if the O-ring is damaged, however slightly, it will prevent the airflow from sucking the paint from the cup. If you aren't already doing it, I strongly recommend the frequent flushing of the airbrush with cleaning fluid (as opposed to thinners) during your painting session.