Cause: The default cell reference style (A1), which refers to columns as letters and refers to rows as numbers, was changed.
Solution: Clear the R1C1 reference style selection in Excel preferences.
Difference between A1 and R1C1 reference styles
On the Excel menu, click Preferences.
Under Authoring, click General .
Clear the Use R1C1 reference style check box.
The column headings now show A, B, and C, instead of 1, 2, 3, and so on.