public partial class Form1 : Form
    {
        [DllImport("User32.dll")]
        public static extern bool LockWorkStation();

        [DllImport("user32.dll")]
        public static extern bool ExitWindowsEx(uint flag, uint reason);

        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            LockWorkStation();
        }

        private void button2_Click(object sender, EventArgs e)
        {
            ExitWindowsEx(1, 0);
        }
    }