Thanks for the responses. I was quite frustrated when I posted my second post.

As far as I can tell, the cold and dark and APU running states are working ok for me, albeit I have not tried to start the aircraft up and fly it from those states yet.

The ready for takeoff state is not working though. The engines are not started and the PFD and ND display are blank.

That is the same after unsinstalling, new download, restarting PC, installing from new download with windows defender off, restarting PC and launching P3D v5.3HF1.

it would be good if there is a solution to this.