This guide will show you how to fix the annoying screen flickering that occurs when running Stronghold HD on Windows 10. It will also probably fix the game not launching.
1. Right-click Stronghold HD in your Steam library, and click “Properties”
2. Select “Browse Local Files”
3. Select Stronghold.exe in the game’s directory, right-click it, and click “Properties”
4. Click the Compatibility tab at the top of the newly opened properties window, and select “Change settings for all users” (you must have admin privileges to do this)
5. Check the box for Run this program in compatibility mode and select Windows 7, and also check the box for Run this program as an administrator, click Apply and then OK
6. Return to the General tab, check the box for Read-only, click Apply and then OK
Now launch Stronghold HD through Steam. The screen flickering should be gone. This will probably also fix your game not launching as well.