+ 0 Votes Format cells traftery 4 years ago Right-click on the cells you want to include in the formula, then select Format Cells. Make sure these cells are formatted as numbers. If the cell type for each cell is already in a number format, then make sure there isn't an apostrophe in front of the number, which would change it to a string. + 0 Votes Excel Formula Question rjohnson 4 years ago Yeah it's most likely a corrupt file. + 0 Votes Excel gremlins liz.lightfoot Updated - 4 years ago Sometimes an Excel worksheet has hidden gremlins--and no matter what you do you can't get the function to work or the right format to display, esepcially with data exported from a database. When I encounter this, I open a new Excel spreadsheet. If your actual data are simply columns of numbers (no formulas that need retaining), you can simply copy your columns of data and 'paste special', values only, into the new worksheet. Then try to sum the 3 columns, with the right cell format of course. It usually works for me.