You might have something very, very far away, so the zoom to fit zooms very far out...
With all the layers visible and unlocked, renovation filter on Show All, open the 3D window, click on Show All for good measure, and with the arrow tool active, hit CTRL-A.
That selects ALL. If your selection shows zero, then sorry... if it shows a number of items, that you expect, and you see a dot lost somewhere in the blankness of the 3D view, then your model is there, and you have to find the culprit.
I would go tool by tool (activate tool, CTRL - A in 3D window) and check... all walls, all slabs, all objects, all roofs, all beams... etc.)
Also, are all of your views in the view set "zoom to fit" or zoomed? If the Ignore zoom box is ticked, then never mind...
If all of this is faster than just redoing the thing?
ArchiCAD since 4.55 ... 1995