Tough break.
How are you trying to view the 3D?
Are you making an axonometric view or a perspective?
If it is a perspective and you don't see anything, it is probable that the camera is aimed wrong.
Your best way to fix this is to place a camera in the plan using the camera tool and aim it at the model. Select it and THEN ask for a 3D view.
Since you are new, I might also ask you a really basic question: Are you actually making 3D elements, like walls, in your plan?
Dwight Atkinson