If the mouse cursor is not visible in-game, please put the the game in Windows Compatibility mode.

To do this right click on the .exe file and select properties. The exe is usually located here -
C:\Program Files (x86)\Steam\steamapps\common\Stronghold

Once you have located the .exe, right click on the exe and select Properties. Tick on 'Run this program in compatibility mode for:' and select 'Windows XP SP3' or 'Windows 7' press Ok. Then run the game as normal via Steam or by double clicking on the exe file.