Completely lost in 3D View

I’ve somehow completely lost my ability to find anything in 3D View. Shift+C doesn’t do anything to the camera. I can find individual objects by selecting them in the outliner and going into local view. I must have hit something and I don’t know how to undo it.

I seem to be able to find an object by using ‘View Selected’ on it, but pressing Shift+C messes up the camera again.

Here is the file:

Any help would be appreciated.

Actually, I believe I’ve found the culprit. One of my objects (expansion link) had infinite dimensions. When I applied the scale it ended up with a scale of 0 on the Y-axis. Fortunately I had an old version backed up with the same object. I don’t know how I would have gone about solving it otherwise.