On every flight after about thirty minutes, all my screens go black. I go to the overhead and flip a couple of switches to bring them back on. How can we avoid that problem from happening?

You are switching power over to the generators when you do that, that's why your screens come back to life.  Best to check out the help documentation that came with the AC.  You'll find there are section's on procedures and checklist's.  

 

Better yet, try the tutorial if it has one.