Some things you might try/investigate.
-- in the future, remember Ctrl+Z is our friend.
-- also in retrospect, 'Save As' might have given you more recovery options out of the mess, later either reverting to last saved or Opus autosaved version.
-- what happens when you create a new Chapter and new Page. Is the problem confined to that one old Page?
meanwhile:
You might try working from the organizer view.
-- first check that some Master Page is not used... applying a transparent background. (unlikely)
-- take a look at any and all Frames. Check their 'Fill' properties, and whether any are 'large' and in the forefront. Look for any Frame or Objects that might be 'hidden' at runtime,
or 'concealed in editor'.
-- also, if you inadvertently dragged an object into a Frame, it could seem to disappear depending on its settings. (not likely you did that for 'all' objects?)
It's possible something in the Pub got corrupted -- sometimes can create a new Pub and set it up for same layout & size, etc. Then back in the 'errant' Pub, copy all objects from 1 Page and Rt-Clk >> Insert Into... in that new Page.
If the problem's not in Opus, you could try
-- taking Windows back a day or so with System Restore
or
-- Uninstall your Graphics/Display device over in Device Manager, shut-down and reboot. Try Opus again.
You might get DW folks to look at the Pub or Page -- in case home remedies don't work.