Use WindowState to make full screen window, change resize mode to NoReSize

   
  
<Window x:Class="_360Timer.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Concentric Rings" Width="910" Height="512">
  <Canvas Name="MainCanvas" Background="#FFE0E0E0"/>
</Window>
//File:Window.xaml.cs


using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Media;
using System.Windows.Shapes;
using System.Windows.Media.Animation;


namespace _360Timer
{

    public partial class Window1 : Window
    {
        System.Windows.Threading.DispatcherTimer frameTimer;
        private int lastTick;
        private Random rand;

        public Window1()
        {
            InitializeComponent();

            this.WindowState = WindowState.Maximized;
            this.WindowStyle = WindowStyle.None;
            this.ResizeMode = ResizeMode.NoResize;
        }

        void Window1_KeyDown(object sender, System.Windows.Input.KeyEventArgs e)
        {
            if (e.Key == System.Windows.Input.Key.Escape)
                this.Close();
        }
    }
}