MediaElement控件的问题(WPF中)?

Question

我想用MediaElement播放视频文件,但是运行后没有反应,也没有报错,请问大家有没有遇到过这种情况?
<Window x:Class="WpfApplication3.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="300" Width="300" Loaded="Window_Loaded">
    <Grid>
        <MediaElement Margin="12,12,12,50" Name="mediaElement1" Stretch="Fill" LoadedBehavior="Manual" Source="M\200712190410116728750.mp3" />
        <Button Height="23" HorizontalAlignment="Left" Margin="12,0,0,12" Name="button1" VerticalAlignment="Bottom" Width="75" Click="button1_Click">Button</Button>
    </Grid>
</Window>...
private void button1_Click(object sender, RoutedEventArgs e)
        {
            //this.mediaElement1.Source = new Uri(@"d:\res\200712190410116728750.mp3");
            this.mediaElement1.Play();
        }