Bob,

I had this problem a long time ago, the  below fixed it, give it a look:

1. Have Excel open.
2. Press “alt+f” to open the file menu then press “t” for the options.
3. Press “control+tab” until the focus is on the “Advanced” options page.
4. Press “alt+e” to toggle the “Allow editing directly in cells”
option. Ensure that this is unchecked.
5. Press “enter” to save the changes.
Editing cell contents should now work again.
Note that in turning this setting off, does change things slightly for visual users:
• With editing directly in cells enabled, when F2 is pressed, the caret appears in the cell itself. Text which would flow out of the cell flows to the right, then to lines below.  Cells covered by this text are hidden while this happens. Text in the edited cell is coloured to highlight cell references and parenthesis.
• With editing directly in cells disabled, when F2 is pressed, the caret appears in the formula bar above the worksheet.  Colouring of formula elements is also done in the formula bar rather than the cell while editing.
Only text which fits in the cell is visible in the cell while the formula is being edited.

I hope this helps,
Al