Using Excel 2003, I chose the menu option Insert - Comment. The comment
field opened, with my user name. I attempted to select all text in the
comment with the key combination Ctrl-Shift-Home, and somehow hit other keys,
because I ended up on the previous worksheet. So, I must have at least hit
Ctrl-PageUp. However, now the Insert - Comment option is disabled
(greyed-out) for that workbook. So are Insert - Hyperlink, - Chart, -
Diagram, - Symbol, and - Object. These options are disabled everywhere in
the workbook. However, I can start an entirely new workbook, and these
options are not disabled. Wha' happen?