c#讓電腦鎖定、注銷、關機

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using Microsoft.Win32;
using System.Runtime.InteropServices;
using System.IO;
using System.Threading;
using System.Diagnostics;


      // 鎖定計算機.   
[DllImport("user32.dll")]
private static extern void LockWorkStation();//須寫extern
private void button1_Click(object sender, EventArgs e)
      {
        LockWorkStation();
      }
//注銷計算機
        [DllImport("user32.dll", EntryPoint = "ExitWindowsEx", CharSet = CharSet.Ansi)]
        private static extern int ExitWindowsEx(int a,int b);
        private void button1_Click(object sender, EventArgs e)
        {
            ExitWindowsEx(0, 0);
        }
//關閉計算機.
private void button3_Click(object sender, EventArgs e)
        {
            System.Diagnostics.Process mp = new System.Diagnostics.Process();
            mp.StartInfo.FileName = "cmd.exe";
            mp.StartInfo.RedirectStandardInput = true;
mp.StartInfo.RedirectStandardOutput = true;
            mp.StartInfo.RedirectStandardError = true;
            mp.StartInfo.UseShellExecute = false;
            mp.StartInfo.CreateNoWindow = true;
            mp.Start();<