Are there indications that the washer has power? lights, anything?

ok, how can you be sure there is power to the unit? Sorry to ask what may seem like a stupid question, but there are reasons for them.

The first place I would look is at the junction box where the house wiring or power cord connects to the d/w, you may have a bad nuetral wire at the wire nut. Check for burn marks at the wire nuts.

I didn't say bad ground :) Bad nuetral...There is a power cord from the wall outlet that connects to the dishwasher at the bottom front left side. This powercord has 3 wires, line nuetral and ground that connects to the diswasher black white and green wires in the little metal box. These wires are joined together via wire nuts. You need to remove the lower access panel of the dishwasher and locate the metal box on the left side. Take the cover off and there are your wires. make sure everything there looks good. You can have a loose connection there, and even though your Plumber said it was live, that does not mean there is not a problem there. Unplug the dishwasher first, then go to that little box and inspect the wiring connections. If the dishwasher is hard wired and not plugged into an outlet, turn power off at the breaker first.

ok, the very first thing that must be done is to verify indeed you have voltage there before I can go further. Sorry if I don't trust your plumber. Also the disposer has nothing to do with the D/W. It is totally seperate, so to proceed further you will need a volt meter, do you have one?