How do I get my idl40 diswasher to heat again?

My idl40 indesit dishwasher has stopped heating. With my dad's help we have changed the heating element, the thermostat, part of the pcb (the white/black box, something to do with a switch?), checked any circuits we can find and made sure everything that should be connected and plugged in is. But it still doesn't heat up! I know it was a cheap model but I would still rather fix it if possible cos can't afford to buy another at the mo! Any help will be greatly received!