Formulas are not updating as I change data

The formulas in the spreadsheet are not updating, IE calculating new results, as I enter new values in source cells. Spreadsheet is a re-named copy of a sheet that does work. Each has a pivot table, for calculating and displaying sums per product. The formulas are basic, IE time difference between 2 cells; convert h:m to decimal value; copy data in another cell (formatted to dd-mmm-yy), formatted to dd; etc). Seems like nothing is working, even if I re-type the formula. ???

Roy, thank you so much. problem solved immediately. Bless you!