I have a worksheet built by someone else with many macros built in and
they all are operational - no error messages.  I want to edit one macro
in the worksheet.  I follow the steps:  Tools, Macro, Macros (here I
get the list of macros in the spreadsheet).  I select the name of the
one in the list that I want to edit then select "Edit" and nothing
happens.  The macro window closes and I'm back in the worksheet.
Microsoft Visual Basic does not open and there is no error message.

As a test, I recorded my own macro in the worksheet then followed the
same steps above but selected my test macro from the list and then
selected "Edit".  When I did this, "Edit" worked as expected.
Microsoft Visual Basic opened and my macro code was displayed.  I was
able to edit the macro code, save it and run it.

Why can't I edit the previously existing macros?