Play button is not responding

Hi Guys

I just downloaded the demo version of Unity 3.1.0 from this website. The problem is that when I click on play button, after doing all the assets placement and other work, to play the scene it does nothing. I watched the tutorial "Working with" but still I am not able to play my scene.


You might not have a camera.

You might have to restart Unity.

You might not have a controller to move around.

But most likely you don't have a camera.