The first thing you need to do is to find a game executable file. Here is the path:

- C:\Program Files (x86)\Steam\steamapps\common\Hitman Contracts

NOTE: For you, a path can be different. In that case just find Steam folder in Program Files and there must be game folder with executable file.

The next step you should do is to start game in Compatibility mode. Here:

-Right-click the game executable file.
-Click Properties.
-Click the Compatibility tab.
-Enable the option Run this program in compatibility mode for:
-Select the compatible Operating System from the drop-down menu.
-Click Apply.