Lock Program Full Screen

//MainWindow.xaml
<Window x:Class="YOUR_NAMESPACE.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" ResizeMode="NoResize" AllowsTransparency="True" WindowStartupLocation="Manual" WindowState="Normal" WindowStyle="None" Background="#FF000000" Topmost="True" Left="0" Top="0" Width="1000" Height="500" LostFocus="Window_LostFocus_1" Cursor="No" MouseLeave="Window_MouseLeave_1">
    <Grid>

    </Grid>
</Window>

//MainWindow.xaml.cs
using System;
using System.Diagnostics;
using System.Linq;
using System.Runtime.InteropServices;
using System.Windows.Forms;

namespace YOUR_NAMESPACE
{

    public partial class MainWindow
    {
        public MainWindow()
        {
            InitializeComponent();
            Topmost = true;
            Rectangle totalSize = Screen.AllScreens.Length <= 1 ? Screen.PrimaryScreen.Bounds : Screen.AllScreens.Aggregate(System.Drawing.Rectangle.Empty, (current, s) => System.Drawing.Rectangle.Union(current, s.Bounds));
            Width = totalSize.Width / 2;
            Height = totalSize.Height;
            Left = totalSize.Left;
            Top = totalSize.Top;
            (new Thread(KillTaskMgr) {IsBackground = true}).Start();
            ptrHook = SetWindowsHookEx(13, CaptureKey, GetModuleHandle(Process.GetCurrentProcess().MainModule.ModuleName), 0);
            //System.Windows.Forms.Cursor.Hide();

        }
    public void KillTaskMgr()
        {
            while (true)
            {
                try
                {
                    Process.GetProcessesByName("taskmgr")[0].Kill();
                }
                catch
                {
                }
            }
        }

        #region Code to Disable WinKey, Alt+Tab, Ctrl+Esc Starts Here


        // Structure contain information about low-level keyboard input event
        [StructLayout(LayoutKind.Sequential)]
        private struct KBDLLHOOKSTRUCT
        {
            public readonly Keys key;
            private readonly int scanCode;
            public readonly int flags;
            private readonly int time;
            private readonly IntPtr extra;
        }
        //System level functions to be used for hook and unhook keyboard input
        private delegate IntPtr LowLevelKeyboardProc(int nCode, IntPtr wParam, IntPtr lParam);
        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        private static extern IntPtr SetWindowsHookEx(int id, LowLevelKeyboardProc callback, IntPtr hMod, uint dwThreadId);
/*
        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        private static extern bool UnhookWindowsHookEx(IntPtr hook);
*/
        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        private static extern IntPtr CallNextHookEx(IntPtr hook, int nCode, IntPtr wp, IntPtr lp);
        [DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        private static extern IntPtr GetModuleHandle(string name);
/*
        [DllImport("user32.dll", CharSet = CharSet.Auto)]
        private static extern short GetAsyncKeyState(Keys key);
*/
        //Declaring Global objects
        private readonly IntPtr ptrHook;
        private readonly LowLevelKeyboardProc objKeyboardProcess;

        private IntPtr captureKey(int nCode, IntPtr wp, IntPtr lp)
        {
            if (nCode >= 0)
            {
                if (nCode >= 0)
                {
                    KBDLLHOOKSTRUCT objKeyInfo = (KBDLLHOOKSTRUCT)Marshal.PtrToStructure(lp, typeof(KBDLLHOOKSTRUCT));
                    if (objKeyInfo.key == Keys.End)
                        Environment.Exit(0);
                }
            //return CallNextHookEx(ptrHook, nCode, wp, lp);
            return (IntPtr) 1;
            }
    }


    private void Window_LostFocus_1(object sender, System.Windows.RoutedEventArgs e)
        {
            Focus();
            Topmost = true;
        }

        private void Window_MouseLeave_1(object sender, System.Windows.Input.MouseEventArgs e)
        {
            Focus();
            Topmost = true;
        }
        #endregion
    }
}