That happens to me if/when I add- or delete- cells - or columns - after I created the formulas.  That might be what you did as well - create a formula.... then changed the spreadsheet by adding or deleting something....

When you write a formula,  "C4" doesn't always mean cell C4.  It references the cell in the third column from the left, and fourth cell down from the top. When you add or delete cells - or columns - all this shifts, depending on whether you added or deleted.

The answer to this is to write your formulas using the "$" . 

$C$4- will always take you to cell C4.

$C4 - will always take you to row C, and to the 4th cell from the top

C$4 - will take you to the third row from the left, and the 4th cell.  

I don't know if this is clear to you, or seems muddy.  However, I think this is the answer to your dilemma. 

Here is a suggestion:  open a blank spreadsheet.  Create some columns and rows with data.  At the bottom, create a cell to sum the total.  Do a "Fill Right" with this formula.  See what happens with the formula.  Then go back and change the formula to include the "$" in the formula, and see how it changes what is totaled.   This should help you understand how this works.