Nothing appears when trying to render, hangs on 'Occlusion preprocessing' My file won't render. My last file rendered fine and when I pressed F12 just to have a idea of how it looked. But now when I'm finished it won't render anything at all. I'm using Blender 2.72 and I'm new to blender. It just stays like this when i try to render.
It's still preparing. Notice the progress indicator in your screenshot:



This will often take a long time when rendering effects like indirect lighting (sometimes I've had it take up to 10 minutes), especially on large scenes.

To help reduce this time, try disabling some effects in the world panel, or increasing the error tolerance: