Wait a second! Cocking lever is supposed to bring the mirror DOWN. If it's already down, the lever will move only a very little.
When you fire the shutter, the mirror will go UP.
Do this. Make sure the dark slide is out. There is a little lever by the film winding lever. Move it so that a red dot shows up. Align the dot on the shutter release with white dot.
Push the shutter.
Did the mirror go UP?