I'm having an issue on a vast scale with WPF Expanders. I have an expander, which contains a stack panel, which contains labels and comboboxes. However, when I run my application, clicking the expander button does nothing :( I click, the direction of the button changes, but nothing displays. What am I doing wrong???

<Expander Header="Vendor" Height="23" Margin="57,0,123,80" Name="expander_Vendor" VerticalAlignment="Bottom" Expanded="expander_Vendor_Expanded">
            <StackPanel Height="100" Name="stackPanel_Vendor" Width="200">
                <Label Height="28" Name="label4" Width="120">Country</Label>
                <Combobox Name ="Country"></Combobox>
            </StackPanel>
        </Expander>