Changing the volume moves the slider, but not the audio output

I have a slider and a webbrowser object in my form and moving, it should change the volume, however it moves the slider as shown here:

but it does not change the actual output of the volume. This is probably due to the fact that I integrated the WebBrowser object and used Windows 7. When I manually move the slider (the one shown in the screenshot), the volume output changes. When playing a WAV file, the volume output changesbut not with a WebBrowser object.

I am using the following code:

Xaml

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Slider Minimum="0" Maximum="10" ValueChanged="ValueChanged"/>
    </Grid>
</Window>

WITH#

public partial class MainWindow
{
    public MainWindow()
    {
        InitializeComponent();
    }

    private void ValueChanged(object sender, RoutedPropertyChangedEventArgs<double> e)
    {
        // Calculate the volume that being set
        double newVolume = ushort.MaxValue * e.NewValue / 10.0;

        uint v = ((uint) newVolume) & 0xffff;
        uint vAll = v | (v << 16);

        // Set the volume
        int retVal = NativeMethods.WaveOutSetVolume(IntPtr.Zero, vAll);

        Debug.WriteLine(retVal);
    }
}

static class NativeMethods
{
    [DllImport("winmm.dll", EntryPoint = "waveOutSetVolume")]
    public static extern int WaveOutSetVolume(IntPtr hwo, uint dwVolume);

}