Suppose column A contains numbers and zeroes in random order.
I want to create a formula in Column B where in case the value of the Column A for the specific row is non zero, it will produce the sum of that cell in Column A plus the three non zero cells of column A above that row.

For example

Column A contains the values, the non zero being e.g. A6, A9, A10, A14

Column B will sum for example in cell B14 (which is adjacent to the non-zero value at A column), A14 plus the three non zero cells above A14, ie A6+A9+A10

confirm with CTRL+SHIFT+ENTER and copy down column

If there aren't 3 non-zero numbers above you just get blanks, see attached example where A1 has random zeroes/non-zeroes. Press F9 to re-generate random numbers

=IF(A6>0,A6+INDEX(A:A,LARG