I'm a newbie to the Capt Sim C130 and I've experienced every symptom you’ve described in your post. I know how you feel!
The answer to your problem is….you must ensure the generators are turned on.

Even if you start your flight with the engines running, you must go back and turn the generators on! It does not make sense to me, but that is how I solved the problem. Hope it works for you. All the best.