Please help, this is my problem. Some formulas don't work when I type them in. For example, when I type this formula, it will say there is an error. "=SUM(1,2,3)" That does not work, it says invalid format. but if I do a formula with a range (instead of commas), it works. Such as "=SUM(A5:C5)" - that works just fine. I am guessing this has something to do with the commas in the formula. When I start to type a formula, a formula helper thing will be displayed that is showing the format of the formula. This format example does not include commas. It uses spaces instead. So I tried to type the formula with spaces (instead of commas) and that doesn't work either. I consider myself a advanced user of excel, I have extensive experience with excel formulas, so this is really bothering me (especially since I can't type many formulas because they need commas and that doesn't work). One more thing. I have existing spreadsheets that I am using (I have created these months ago). On these, I have formulas that contain commas and they all work. But if I double-click on the cell (as if I am going to edit the formula, but I don't edit it, I keep it the same) and press enter, the same error appears. If I hit escape, it cancels the formula edit request and goes back to how it was. I did try to uninstall and reinstall excel, that didn't work. But I think it is still pulling my info from somewhere. Thanks for all of your help.