Excel 2003

This is a weird problem that I've never seen before.  We have a user who is
unable to view the contents of a specific Excel workbook.  When the user
opens the file it looks as if there are no files open--all he gets is a gray
screen with the menu and toolbars.  The name of the file does not appear in
the title bar and there are no sheet tabs at the bottom of the screen
either.  So it looks like no file has been opened.  But there are some
telltale signs that the file IS actually open.  The Name box shows "A25" and
the Formula box shows the value of that cell, and those values change as the
arrow keys are used, showing that the cursor is moving around in an open
spreadsheet even though the cursor itself cannot be seen.  The Font box
displays "Arial" and the Font Size box shows "12," and finally hitting the
Print Preview button shows the entire contents of the spreadsheet.  So the
file is definitely open, but it looks like nothing is there.

Other people are able to view the workbook without any problems, so I know
that it's not a problem with the workbook, and the user can view other
workbooks just fine, so it would seem that the problem is not with his Excel
installation.  There are no macros in the workbook, and no locked, hidden,
or protected cells.  The fact that even the sheet tabs at the bottom of the
screen cannot be seen rules out the "background color is the same as the
font color" problem.

The user reports that he was able to view the workbook up until last week,
at which time he "hit something" and he has not been able to view the file
since.  Of course, he has no idea what he hit.

I'm stumped.  Any help will be greatly appreciated!

--Tom