SUMIF random cells

I want to add up cells only if they are more than 0. I can do this if it is a range of cells but i can't add them if it is just a string of cells.

for example

add Y1323+Y1330+Y1337+Y1344+Y1351+Y1358+Y1365+Y1372+Y1379+Y1386+Y1393+Y1400+Y1407+Y1414+Y1421+Y1428+Y1435+Y1442+Y1449+Y1456+Y1463+Y1470+Y1477+Y1484+Y1491 only if the contents of the cell is greater than 0

You say that the cells are random but in your example they're every 7th row so you could use this formula

=SUMPRODUCT(--(MOD(ROW(Y1323:Y1491)-ROW(Y1323),7)=0),--(Y1323:Y1491>0),Y1323:Y1491)

Mr Long legs,
Thanks for this, it works. However I have another question. I would now like to count each cell (every 7 rows) with a number greater than zero in it.
I have tried to work it out on my own but it keeps telling me that my argument is too long. Any thoughts?

Thanks