You need to set the Visible property of all three combo boxes in each button's Click event procedure. So in the first button's Click event procedure:
Me.[FirstComboBox].Visible = True
Me.[SecondComboBox].Visible = False
Me.[ThirdComboBox].Visible = False
in the second button's:
Me.[FirstComboBox].Visible = False
Me.[SecondComboBox].Visible = True
Me.[ThirdComboBox].Visible = False
and in the third button's:
Me.[FirstComboBox].Visible = False
Me.[SecondComboBox].Visible = False
Me.[ThirdComboBox].Visible = True
Ken Sheridan, Stafford, England