I tried changing the Display options, but that wasn't it. And there are no macros active.

I did a little experiment:

Scenario 1: I launch Excel and open Spreadsheet A. It's blank (my current problem).
Scenario 2: I launch Excel and open a blank spreadsheet. THEN I open Spreadsheet A, and it's now visible and working fine.

Does this help shed some light on the situation?

Thanks for your help!