Do you have windows that don't show in plan view because they are too high above the cut plane? Do you have a fireplace opening that doesn't show because it's too far below the cut plane? Use the Plan Region Tool in your View Tool Palette. With this tool you can set a unique view range to include objects above or below the cutting plane that's set in the given view.
Once plan regions are placed they can often be difficult to locate. Select one you can find and Edit it. You'll notice that all the other plan regions are now visible.