Why doesn't my dishwasher power on?
I believe the electrician also disconnected another wire, from the neutral bus bar, in addition to the "two wires from two circuit breakers" you mentioned.

Follow the two you mentioned to where they exit the wall or the main panel and find a third there.  That (white) one is probably not connected to anything, but should be connected to the neutral bus bar.

Here is my rational:

Stoves use two hots.  Old stoves especially, only use two hots to operate.

Dishwashers need a hot and a neutral.  

If the electrician disconnected a sub-panel, he probably did it all the way, not just the hots.  You should check for and reconnect an uninsulated ground conductor as well if its loose in the main panel.

If the neutral was not connected, the stove would work, and the dishwasher not.