Months after I left my Bootcamp demo alone, I can't see anything anymore..

When I press the play button, I see on the scene that the soldier is stuck awkwardly on the ground like the Leaning Tower of Pisa and that I can't see anything from the game view, and I can't walk or run around. I am a complete beginner just downloading demos to run them on my PC. I think I messed up the third-person camera and I don't know how to put the thing back to normal. Please help.