For some reason all of a sudden when I update cells in Excel, my equations are not being updated. For example, I have a simple equation =SUM(C4:C16)
. If I change any of the cells in C4C16, the answer doesn't get updated... I don't know what happened I've never seen this fail before. Any ideas?



Check to make sure Automatic Calculation is still selected. Go to Formulas>Calculation>Calculation Options and select "Automatic". 


Try changing the format type of the calculated cell from "Text" to "General" and then reenter the formula. That fixed the problem when I was seeing these symptoms. 


Usually changing the "Workbook Calculation" option (Excel 2010) solves the problem, but if it didn't, probably the workbook itself is set to manual calculation. To change this, open the workbook, select the "Formula" tab (Alt+M), then click "Calculation Options" and the select "Automatic". Now save the workbook. 


I think this can happen when you end up with different data types in the fields in the given range. Can you check and make sure the data in there is all still numerical? I think I've noticed this happening for me when I threw in a value once that was "$xyz" as opposed to "xyz" (I mean xyz to be some integer, of course). 


It's like it gets stuck. I suggest you copy your formula into Notepad, then type any number into the cell. After that, click on the cell and paste your formula into the formula bar and hit enter. That resolved the problem for me. 

