I think the 3D view is viewing the ground or a place where there's nothing to see.
Please, read the help about 3D view or the user's guide http://www.sweethome3d.eu/userGuide.html#editing3DView to see how you can navigate in the 3D view.

If you still have some problems, you can send me your SH3D file at [url=mailto:[email protected]][email protected][/url] to let me see what's the problem.