=== MainWindow.xaml ===

<Window x:Class="WpfApp3.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApp3"
        mc:Ignorable="d"
        Title="5 in a row" Height="450" Width="600">
    <Grid>
        <TextBlock x:Name="textBlock" HorizontalAlignment="Center" Margin="163,74,135,0" Padding="20" TextWrapping="Wrap" Text="If you get 5 dots in the same color, you've won." VerticalAlignment="Top" Height="67" Width="294"/>
        <Image x:Name="image1" HorizontalAlignment="Left" Height="40" Margin="149,178,0,0" VerticalAlignment="Top" Width="40"/>
        <Image x:Name="image2" HorizontalAlignment="Left" Height="40" Margin="206,178,0,0" VerticalAlignment="Top" Width="40"/>
        <Image x:Name="image3" HorizontalAlignment="Left" Height="40" Margin="263,178,0,0" VerticalAlignment="Top" Width="40"/>
        <Image x:Name="image4" HorizontalAlignment="Left" Height="40" Margin="321,178,0,0" VerticalAlignment="Top" Width="40"/>
        <Image x:Name="image5" HorizontalAlignment="Left" Height="40" Margin="378,178,0,0" VerticalAlignment="Top" Width="40"/>
        <Button x:Name="button" Content="Start game" HorizontalAlignment="Left" Margin="244,319,0,0" VerticalAlignment="Top" Width="102" Click="button_Click"/>
        <MediaElement x:Name="mediaElement1" HorizontalAlignment="Left" Height="51" Margin="417,288,0,0" VerticalAlignment="Top" Width="51" LoadedBehavior="Manual" Source="C:\Users\User\source\repos\WpfApp3\WpfApp3\bin\Debug\sounds\bleep.mp3"/>
        <MediaElement x:Name="mediaElement2" HorizontalAlignment="Left" Height="51" Margin="492,288,0,0" VerticalAlignment="Top" Width="51" LoadedBehavior="Manual" Source="C:\Users\User\source\repos\WpfApp3\WpfApp3\bin\Debug\sounds\door_buzzer.mp3"/>
        <Label x:Name="timerLabel" HorizontalAlignment="Left" Margin="40,288,0,0" VerticalAlignment="Top" Height="51" Width="168"/>
    </Grid>
</Window>

.....

=== MainWindow.xaml.cs ===

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Threading;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Media;

namespace WpfApp3
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        DispatcherTimer dt = new DispatcherTimer();

        public MainWindow()
        {
            InitializeComponent();

            BitmapImage bi1 = new BitmapImage();
            bi1.BeginInit();
            bi1.UriSource = new Uri("C:/Users/User/source/repos/WpfApp3/WpfApp3/bin/Debug/images/greendot.png", UriKind.Absolute);
            bi1.EndInit();

            image1.Source = bi1;
            image1.Visibility = Visibility.Collapsed;
            //image1.Visibility = Visibility.Visible;

            BitmapImage bi2 = new BitmapImage();
            bi2.BeginInit();
            bi2.UriSource = new Uri("C:/Users/User/source/repos/WpfApp3/WpfApp3/bin/Debug/images/greendot.png", UriKind.Absolute);
            bi2.EndInit();

            image2.Source = bi2;
            image2.Visibility = Visibility.Collapsed;
            //image2.Visibility = Visibility.Visible;

            BitmapImage bi3 = new BitmapImage();
            bi3.BeginInit();
            bi3.UriSource = new Uri("C:/Users/User/source/repos/WpfApp3/WpfApp3/bin/Debug/images/greendot.png", UriKind.Absolute);
            bi3.EndInit();

            image3.Source = bi3;
            image3.Visibility = Visibility.Collapsed;
            //image3.Visibility = Visibility.Visible;

            BitmapImage bi4 = new BitmapImage();
            bi4.BeginInit();
            bi4.UriSource = new Uri("C:/Users/User/source/repos/WpfApp3/WpfApp3/bin/Debug/images/greendot.png", UriKind.Absolute);
            bi4.EndInit();

            image4.Source = bi4;
            image4.Visibility = Visibility.Collapsed;
            //image4.Visibility = Visibility.Visible;

            BitmapImage bi5 = new BitmapImage();
            bi5.BeginInit();
            bi5.UriSource = new Uri("C:/Users/User/source/repos/WpfApp3/WpfApp3/bin/Debug/images/reddot.png", UriKind.Absolute);
            bi5.EndInit();

            image5.Source = bi5;
            image5.Visibility = Visibility.Collapsed;
            //image5.Visibility = Visibility.Visible;

            /*
            image1.Visibility = Visibility.Collapsed; // image hidden
            image1.Visibility = Visibility.Visible; // image visible        
            */
        }

        private void button_Click(object sender, RoutedEventArgs e)
        {
            button.Visibility = Visibility.Hidden;
            //button.Visibility = Visibility.Collapsed;
            test();         
        }

        public void test()
        {
            //DispatcherTimer dt = new DispatcherTimer();
            //dt.Interval = TimeSpan.FromSeconds(2);
            dt.Interval = new TimeSpan(0, 0, 0, 2);
            dt.Tick += dt_Ticker;
            dt.Start();
        }

        private int increment = 0;

        private void dt_Ticker(object sender, EventArgs e)
        {
            increment++;
            String num = increment.ToString();

            if (increment == 1)
            {
                image1.Visibility = Visibility.Visible;

                mediaElement1.Play();
                mediaElement1.Position = TimeSpan.Zero;               
            }

            if (increment == 2)
            {
                image2.Visibility = Visibility.Visible;

                mediaElement1.Play();
                mediaElement1.Position = TimeSpan.Zero;
            }

            if (increment == 3)
            {
                image3.Visibility = Visibility.Visible;

                mediaElement1.Play();
                mediaElement1.Position = TimeSpan.Zero;
            }

            if (increment == 4)
            {
                image4.Visibility = Visibility.Visible;

                mediaElement1.Play();
                mediaElement1.Position = TimeSpan.Zero;
            }

            if (increment == 5)
            {
                image5.Visibility = Visibility.Visible;

                mediaElement2.Play();
                mediaElement2.Position = TimeSpan.Zero;
                dt.Stop();
            }

            /*
             if (increment == 6)
             {                
                 button.Visibility = Visibility.Visible;
                 button.Content = "Exit game";			
				
			   ((DispatcherTimer)sender).Stop();	
             } 
             */

            //timerLabel.Content = "Round " + num;

        }
    }
}