Can you attach the excel file (using the paperclip above where you are typing) or upload to wikisend and copy/paste the id?
Thank you. I am looking at it now and I see what you are talking about.
Okay, so there was a circular reference. Let me explain. The formula in cell C18 was =sum(c13:c21), so excel is trying to sum cells C13 through C21, including C18, where the sum is going. Everytime it sums, C18 updates, so the formula must update, so C18 updates, so the formula updates, etc. When you tried to sum C18 and C19, Excel just gave up, because it can't really compute C18. If you change the sum formula in C8 to sum C13 through C17, =sum(C13:C17), everything seems to work.
Sorry, I meant change the formula in C18. My 1 key is going bad.
Were you purposely trying to do a circular reference (to make a for loop in Excel)? I have done that before if you were trying to do it on purpose.