blender renders nothing i've made a bus model for my little project, on the earlier version of my model it renders just fine, on this version it just doesn't show up in the renderer, just pitch black,on materials and texture its fine, render just shows nothing, here's a screenshot and my .blend file that might help you to understand my problem
You turned off the Combined Layer Pass in the scene

Go to the Properties Editor > Render Layers Tab > Passes and activate the Combined layer pass