"Show all in 3D" will not change the orientation of the view - so if you are looking at nothing, you will still be looking at nothing after invoking this command.
The 'Fit in Window" command should work, even if you are currently not looking at anything.
I just tested and this seems to be the case.
However I am wondering if you have something very far away from you main model.
Try fitting to window and then selecting all (CTRL+A) to see if anything selects.
I see this behaviour in perspective if I place something very far away, but it also affects the axonometric view.
Barry.
One of the forum moderators.
Versions 6.5 to 27
i7-10700 @ 2.9Ghz, 32GB ram, GeForce RTX 2060 (6GB), Windows 10
Lenovo Thinkpad - i7-1270P 2.20 GHz, 32GB RAM, Nvidia T550, Windows 11