求助：设计好程序后点击Button程序没有响应

设计一个计时器，界面设计好后，点击运行能够出现界面，但点击Button按钮程序没有反应，大虾们，帮忙看看呗，代码是下面这样滴
<Window x:Class="计时器.MainWindow"
        xmlns="http://schemas.
        xmlns:x="http://schemas.
        Title="倒数计时器" Height="350" Width="525" FontFamily="MS UI Gothic">
    <Grid>
        <TextBox Height="122" HorizontalAlignment="Left" Margin="84,20,0,0" Name="textBox1" VerticalAlignment="Top" Width="312" Background="#FF343232" Foreground="#FF85DB22" TextChanged="textBox1_TextChanged" FontWeight="ExtraBlack" FontFamily="Verdana" FontStretch="Normal" TextWrapping="WrapWithOverflow" TextAlignment="Center" VerticalContentAlignment="Center" CharacterCasing="Normal" DataContext="{Binding}" Padding="4" Grid.Column="0" Grid.ColumnSpan="1" FontSize="80" />
        <Button Content="十分钟倒计时" Height="40" HorizontalAlignment="Left" Margin="62,172,0,0" Name="button1" VerticalAlignment="Top" Width="150" />
        <Button Content="五分钟倒计时" Height="40" HorizontalAlignment="Left" Margin="62,240,0,0" Name="button2" VerticalAlignment="Top" Width="150" />
        <Button Content="开始" Height="60" HorizontalAlignment="Left" Margin="226,194,0,0" Name="button3" VerticalAlignment="Top" Width="60" Click="button3_Click" />
        <Button Content="清空" Height="60" HorizontalAlignment="Left" Margin="310,194,0,0" Name="button4" VerticalAlignment="Top" Width="60" />
        <Button Content="全屏" Height="60" HorizontalAlignment="Left" Margin="404,194,0,0" Name="button5" VerticalAlignment="Top" Width="60" />
    </Grid>
</Window>