Step 1: Open any Excel file or the file you need to fix and click on File .
Step 2: In the Menu, select Options to enter Excel Options.
Step 3: In Excel Options, select Formulas in the Calculation Options section . Now select Automatic mode and then OK again.
After activating the automatic calculation mode, not only the SUM function but also other calculation functions in Excel will work normally. Especially, if you are a beginner with Excel, mastering the calculation functions will help increase work efficiency. You can refer to other calculation functions in Excel to get familiar with the spreadsheet.