What conditional format expression are you using?
Are all the drop down formatted fields of type text?
Could any of these fields store multiple values instead of just one? (you can select multiple values in a pop up menu by holding down the shift key. THis produces a return separated list of the selected values and can affect whether a calclation using = can determine if a value is selected in it or not.)
I used the value is = to yes and the same for no.
They are all text, it is just yes, no and na.
They are all single values.