Excel 2007 : Sum up cells by cell background color

I am using the following formula:

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I used this in a spreadsheet I had for 2012 and just copied that same spreadsheet to use for 2013 and now my formula won't work. I remember when I first started using it in 2012, I had to hit some key to run the "macro" or formula but then it started doing it itself. How do I get the formula to start working again? I'm using the same cells/formulas as the old spreadsheet, I just updated the days of the year.

hi shelmstr1, press [SHIFT+F9]

Thank you for the reply but that didn't seem to work. Somehow though, one of my rows started working so as long as I copy the cell contents from that row to the other rows I'm trying to add it seems to work.