After upgrading to Windows 10, I found that if you start FSX in windowed mode and then switch to full screen (Alt-Enter) after your flight loads, everything works fine in DX 9.
Just remember to switch back to windowed mode before you end your flight. Kind of a nuisance, I know, but I've had no problems since I started using this technique.
I'm using an Nvidia card, but I think this will still work with AMD cards.
Hope this helps!