How do I use the Sum Function; my result is ### or the text of the function

I changed some of the settings yesterday and now when I use the Sum Function the result shows the text of the function or ###

Column is not wide enough to display result. Widen the column.

You may have also changed the display of formulas. From menu → Tools->Options under LibreOffice Calc->View in right panel under Display remove check for Formulas.

### is an indicator that the calculated number does not fit into the cell. Increase your column width and you’ll see the number.