Problem began without warning - when turning key, instrument cluster flickers (lights are bright when flickering), auto windows intermittently work, radio doesn't, a/c doesn't. Engine starter doesn't engage. Any thoughts?

AC should not work while starting the car.
Look through here:
https://www.askmehelpdesk.com/cars-trucks/

. Ensure battery is fully charged.
. Check all under-dash and under-hood fuses with a test light or multimeter.
. Check ignition switch/harness.