Zoom in timeline not working

[GuySpot]

All of sudden I cannot zoom in or out on the either the multitrack or waveform timelines.  This is wtih the on screen buttons, keyboard and mouse wheel.  I can't fathom what's wrong here.

[SteveG_AudioMasters_]

The only way I'm aware of that this can happen is if the Zoom Factor (Time) setting in Edit > Preferences > General is set to 0%. That effectively stops all zooming, except for using the scroll-zoom bar at the top of the screen. It needs to be set to a sensible value - 35-40%.