Do you have the same issue if you follow the OP’s steps to reproduce it?
Provide extra information to complete the original description of the issue:
Have you tried simply starting on APU? I also could not get ground power to work as I recall. To start, turn on both batteries. You should see 24.0 volts. Click APU and APU start buttons near bottom center of that panel. Then click APU Generator and APU bleed. You should now see voltage going up to 28V and then you can click on the engine bleeds and feed pumps. Finally start engines using the knob and switches behind the throttles. I’m going by memory here, but think I got it all.
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