Sum Cells based on Another Cell

[rwamser]

What I am trying to do is SUM 2 cells ( G40-G39 ) if Cell A40 contains a Date if No Date in Cell A40 then Place a 0 in Cell G40

[starguy]

where do you want to put your formula (in which cell?)
are you sure that you want to put 0 in cell G40?

What I am trying to do is SUM 2 cells ( G40-G39 ) if Cell A40 contains a Date if No Date in Cell A40 then Place a 0 in Cell G40