A strange problem I have never seen before has appeared. I cant get FSX to run in full screen mode. If I press Alt Return or choose full screen from the menu FSX only goes back to windowed mode. I tried deleting the fsx.cfg file and first it worked. FSX started in full screen mode as it used to but after the FSX Fiber Accelerator started FSX got minimized to the task bar and I couldn't maximize it.  I exited FSX. And when I restarted it opened in windows mode which couldn't be changed to full screen. I don't have this problem in FSX-SE or P3D 2.5.

I have the black screen when I toggle to full screen too so I press "S" to go to an outside view, toggle it to full screen, then press Shift+"S" return to cockpit view. See if that works for you. I have no idea why it does this, but it has been that way for years on my system. I suspect it's something Nvidia related but I'm not sure, and does it on two different video cards (both Nvidia).. You have an Nvidia too so maybe it will work for you.

The minimize issue - what I do is press the icon on the taskbar and hold the mouse button down. It will eventually return to full screen (3 or 4 seconds later). Strange, no? Been living with it for years as I said.