Not sure why you can't start the engines, BUT... I wonder if you need to make sure to turn on the Avionics Switch!?

I have this turned on by default by having my default flight as the Cessna C-172 in a cold and dark setting, except that the Avionics switch is turned ON.
Most Captain Sim aircraft don't come with an Avionics switch (737 Captain (FSX/SE/P3D) being the exception), and I have found that this is the best way to guarantee that the Avionics are ON when loading a Captain Sim aircraft.

I did a short (3 min) video today, that I uploaded to YouTube this morning on how I start the engines. It's no different to the 2011 video really, except that I added instructions to it (in the explanation write up).
I don't upload many videos to YouTube anymore, so I don't know how to make them any clearer than how they show up  on there now.
I did the recording at 1920x1080 (maybe I should have used 2560x1440 (my default screen resolution), or perhaps higher to record it. Also, I use Nvidia Shadowplay to record my in-game videos.

New video: https://www.youtube.com/watch?v=52pOwT9Pd0M

Edit ([timestamp=1706232151]). Starting without the Avionics being turned on made no difference to starting the engines for me.  :-?