This course will look at the fundamentals of rendering in Arnold. We'll go through the different light types available, cameras, shaders, Arnold's render settings and finally how to split an image into render passes (AOV's), before we then reassemble it i
Its probably the settings in the envrionment, check that you diplay option allow the displaying of the objects you're trying to view.
The big difference between opening and importing is that when you open it will open the maya file (including the environment). When you import it is importing the contents of the maya file into your current environment (which might have the display>polygons .. etc) set differently.