Hi Winnie,
Have you tried pressing the other Ctrl key on your keyboard to see if that works for crouching?

Edit: I just took a peek at the walkthrough and updated review of this game. The Escape key is used for switching between first and third person. When you press the Ctrl key, check the icon of the figure at the bottom of your screen to see if it is standing or crouching. It could be that it switches to first person when in crouch mode in order to give you a better close-up view.