Aside from verifying your game cache and checking your connection with Steam, you may also need to manually run secondary installers required by this game.
1. Exit Steam entirely.
2. Browse to your Stronghold Crusader 2 installation folder
(Usually - C:\Program files\Steam\Steamapps\common\Stronghold Crusader 2\)
3. Run the following installers:
...\steamapps\common\Stronghold Crusader 2\resources\directx\DXSETUP.exe
...\Steamapps\common\Stronghold Crusader 2\resources\redist\vcredist_x86.exe
...\Steamapps\common\Stronghold Crusader 2\resources\redist\vcredist_2008_x86.exe
...\Steamapps\common\Stronghold Crusader 2\resources\redist\vcredist_x86.exe
...\Steamapps\common\Stronghold Crusader 2\resources\redist\vcredist_2008_x86.exe
Reboot your computer and test any issues again.