=IF Statement to control a drop-down box

I have a drop-down box with about 8 number selections in it. It works fine. However, I want to change this drop-down box depending on a condition in another cell, so that if that other cell has the word "No" in it, it forces the drop-down box to now have a zero in it (ideally then preventing the user from entering anything else in the cell). I have tried using Data validation and the type of source code that is supposed to suppress the drop-down box under the correct circumstances (i.e. that the other cell has "No" in it), but what I then get is the last selected number (a positive integer from the drop-down selection) sitting in the drop-down box, which affects all my 'down-stream' data. What I want is to select "No" in the other cell, which will force the drop-down cell to have a zero in it. I hope that makes sense. The cell with the "No" in it could be thought of as a 'master cell' that overrides any function in the 8-selection drop-down box on the condition that the user has selected "No" in the 'master cell' - on which condition the drop-down box is forced to have a zero in it.