int hwnd;
 hwnd = FindWindow("Progman", null);                
 PostMessage(hwnd, /*WM_QUIT*/ 0x12, 0, 0);
                

        [DllImport("user32.dll")]
        public static extern int FindWindow(string lpClassName, string lpWindowName);
        
        [return: MarshalAs(UnmanagedType.Bool)]
        [DllImport("user32.dll", SetLastError = true)]
        public static extern bool PostMessage(int hWnd, uint Msg, int wParam, int lParam);