Gray cone obscuring/clipping the 3D Viewport When looking at my objects in 3d view I'm seeing a gray cone that seems to be hiding other objects. 

Can anyone help me turn this off and explain what it is please.

Screenshots attached.
You somehow enabled the clipping region (or clipping border). It's created in 2D, but projects into 3D, thus it looks like a cone from certain angles.
Disable it by clicking View &gt; View Region&gt; Clipping Region... in 3D View header, or press AltB