You will want to make sure your rendering sub-system is set to Direct3D9.
If you don't like DirectX for whatever reason and want to use OpenGL, then try Qeffects-gl, or ReShade.
You can change your rendering sub-system within the game under the video settings, or go to ogre.cfg in your main Feral-Heart directory, and edit the line so it should be this:
Render System=Direct3D9 Rendering Subsystem
Also, when starting the game, there should be little green text in the top left corner in the screen. That's how you should know that ENB is functioning.