validation based on values of some fields

Hi All.

I would like validate if AccountNo (it include one ComboBox and three TextBoxes) and ServiceDatePicker duplicated. I mean, if database has data, for instance:

AccountNo (123 4567890 5 88) and 1/1/2013 and user will entering the same AccountNo and the same date only at that case all fields of AccountNo and ServiceDatePicker must be validated. How it to do? I will appreaciate for sample.

Thanks.