Maybe you've written some macro with the name "InsertSymbol"?
Or use the keyboard shortcut Ctrl + Alt + Num+ (where Num+ is the "+" key on
the numeric keypad), and then click on "Insert > Symbol".
That could tell you any weird stuff (macro or add-in that took over the
If that doesn't help, resetting the Insert menu might fix it ("Tools >
Customize...", then right-click on the Insert menu).