well there's a good ending here...
after a 1 hour power disconnect in the basement, which was effectuated by pulling a plug that I had put on heavy gauge romex from the d/w and plugs into an outlet located on the wall beneath where the d/w is in the kitchen upstairs (because we didn't have room in the 100 amp box for another separate breaker), we powered on again. Went up stairs, and still no change upon pushing "Start", and must have left the door closed, because 20 minutes later while on the computer the d/w starts to drain, then begins filling. So I let it go thru a complete normal cycle, and no problems. No idea why that happened, or why it was humming loudly the morning of the initial problem, then every the door was opened then closed, the humming continued, but at a much lower level, and continued to do so every time the door was shut but would not start. Now this. Weird, but I'll take it, fingers crossed. Maybe it's a self-healing machine...go figure.