here's the basics for appliance repair. you'll pick up more knowledge as you go along (learning from mistakes) but this should get you going.
when you're not sure whats wrong, you can't afford a repairman, you can't do without the appliance, and the 'magic smoke theory'** has let you down, start out by replacing all parts (in the order of cheapest to most expensive, testing to see if it works after each one) until it works.
** for those novices who don't know the magic smoke theory
the magic smoke theory states that-
all electrical apparatus require magic smoke to operate. when an appliance stops working, open it up and look over the circuits. often, when the magic smoke leaves a part, it stains the surrounding parts and melts or disfigures the part it escaped from. locate and replace the part that has lost it's smoke with a new one (that comes with a full charge of smoke) and it usually fixes the appliance.