Sometimes the camera gets pointed in the wrong direction.
A sure fire solution is to actually place a new camera in your plan view using the camera tool.
Aim the new camera at your model.
Select the camera.
Activate 3D window.
Sometimes the model gets "jammed up."
In this case, you need to verify that you actually can make a 3D view.
Close the 3D window,
switch to Axonometric view.
Activate the 3D window.
Dwight Atkinson