mouse_event LEFTDOWN LEFTUP doesn't working in C#

I have some problem with my code. It can Set cursor position but it can't click. I read some post in this webstie, but I still can't fix my problem. So, what should I do? I am using C# .Net in Microsoft Visual Studio 2013 Ultimate.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Runtime.InteropServices;

namespace AutoClick
{
    public partial class main : Form
    {
        [DllImport("user32.dll")]
        static extern void mouse_event(int dwFlags, int dx, int dy, int dwData, int dwExtraInfo);

        [Flags]
        public enum MouseEventFlags
        {
            LEFTDOWN = 0x00000002,
            LEFTUP = 0x00000004,
            MIDDLEDOWN = 0x00000020,
            MIDDLEUP = 0x00000040,
            MOVE = 0x00000001,
            ABSOLUTE = 0x00008000,
            RIGHTDOWN = 0x00000008,
            RIGHTUP = 0x00000010
        }

        public static void LeftClick(int x, int y)
        {
            Cursor.Position = new System.Drawing.Point(x, y);
            mouse_event((int)(MouseEventFlags.LEFTDOWN), 0, 0, 0, 0);
            mouse_event((int)(MouseEventFlags.LEFTUP), 0, 0, 0, 0);
        }

        public main()
        {
            InitializeComponent();
        }

        private void main_Load(object sender, EventArgs e)
        {
            LeftClick(this.Location.X + 300, this.Location.Y + 250);

        }

        private void button1_Click(object sender, EventArgs e)
        {
            button1.Text = "Ok";
        }
    }
}

You have no code to activate main_load function, unless it's self activated, but when I did this, my window goes away, until I retrieve it from the taskbar.

        private void button1_Click(object sender, EventArgs e)
        {
            LeftClick(this.Location.X + 300, this.Location.Y + 250);
        }

I'm not sure if you are trying to move the window on mouse click, or move the mouse, but since

EDIT ... I now better understand these functions, here's a clean working code.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Form1
{
    public partial class Form1 : Form
    {
        private int posx, posy;
        private int locx, locy;
        private int curx, cury;
        private Rectangle screenRect;
        private Rectangle rect;

        public Form1()
        {
            InitializeComponent();
            codeit();
        }

        private void codeit()
        {

            locx = this.Location.X; locy = this.Location.Y;
            screenRect = Screen.PrimaryScreen.WorkingArea;
            rect = this.RectangleToScreen(screenRect);
            Console.WriteLine(rect.ToString());

            // to avoid clicking outside the window...
            locx += rect.X; locy += rect.Y; // location of window relative to screen
            // It's better to create your own function, so you have complete control of it
            MouseAction("action", "appWin");
        }

        private void MouseAction(string mouseAction, string appWindow)
        {
            switch (mouseAction)
            {
                case "left":
                    mouse_event((uint)MouseEventFlags.MOUSEEVENTF_LEFTDOWN, 0, 0, 0, 0);
                    mouse_event((uint)MouseEventFlags.MOUSEEVENTF_LEFTUP, 0, 0, 0, 0);
                    label1.Text = "left clicked"; Thread.Sleep(1000);
                    break;
                case "right":
                    mouse_event((uint)MouseEventFlags.MOUSEEVENTF_RIGHTDOWN, 0, 0, 0, 0);
                    mouse_event((uint)MouseEventFlags.MOUSEEVENTF_RIGHTUP, 0, 0, 0, 0);
                    label1.Text = "right clicked";
                    break;
                case "middle":
                    mouse_event((uint)MouseEventFlags.MOUSEEVENTF_MIDDLEDOWN, 0, 0, 0, 0);
                    mouse_event((uint)MouseEventFlags.MOUSEEVENTF_MIDDLEUP, 0, 0, 0, 0);
                    label1.Text = "middle clicked";
                    break;
            }
        }

        [DllImport("user32.dll")]
        public static extern void mouse_event(uint dwFlags, int dx, int dy, uint dwData, int dwExtraInfo);

        [DllImport("user32")]
        public static extern int SetCursorPos(int x, int y);

        [DllImport("USER32.DLL")]
        public static extern IntPtr FindWindow(string lpClassName, string lpWindowName);

        [DllImport("user32.dll")]
        private static extern bool MoveWindow(IntPtr hWnd, int X, int Y, int nWidth, int nHeight, bool bRepaint);

        private static bool WindowActive(string keys, IntPtr handle)
        {
            throw new NotImplementedException();
        }

        //________________________________________________________________________________________
        // Input Region Begin
        [Flags]
        enum MouseEventFlags : uint
        {
            MOUSEEVENTF_MOVE = 0x0001,
            MOUSEEVENTF_LEFTDOWN = 0x0002,
            MOUSEEVENTF_LEFTUP = 0x0004,
            MOUSEEVENTF_RIGHTDOWN = 0x0008,
            MOUSEEVENTF_RIGHTUP = 0x0010,
            MOUSEEVENTF_MIDDLEDOWN = 0x0020,
            MOUSEEVENTF_MIDDLEUP = 0x0040,
            MOUSEEVENTF_XDOWN = 0x0080,
            MOUSEEVENTF_XUP = 0x0100,
            MOUSEEVENTF_WHEEL = 0x0800,
            MOUSEEVENTF_VIRTUALDESK = 0x4000,
            MOUSEEVENTF_ABSOLUTE = 0x8000
        }

        ///// <summary>
        ///// Synthesizes keystrokes, mouse motions, and button clicks.
        ///// </summary>
        [DllImport("user32.dll", SetLastError = true)]
        static extern uint SendInput(uint nInputs, ref INPUT pInputs, int cbSize);

        // INPUT
        [StructLayout(LayoutKind.Sequential)]
        struct INPUT
        {
            public SendInputEventType type;
            public MouseKeybdhardwareInputUnion mkhi; // Mouse, Keyboard, Hardware, Input
        }

        enum SendInputEventType : int
        {
            MOUSE = 0,
            KEYBOARD = 1,
            HARDWARE = 2
        }

        [StructLayout(LayoutKind.Explicit)]
        struct MouseKeybdhardwareInputUnion
        {
            [FieldOffset(0)]
            public MouseInputData mi; // mouse input

            [FieldOffset(0)]
            public KEYBDINPUT ki; // keyboard input

            [FieldOffset(0)]
            public HARDWAREINPUT hi; // hardware input
        }

        struct MouseInputData
        {
            public int dx;
            public int dy;
            public uint mouseData;
            public MouseEventFlags dwFlags;
            public uint time;
            public IntPtr dwExtraInfo;
        }

        [StructLayout(LayoutKind.Sequential)]
        struct KEYBDINPUT
        {
            public ushort wVk;
            public ushort wScan;
            public uint dwFlags;
            public uint time;
            public IntPtr dwExtraInfo;
        }

        [StructLayout(LayoutKind.Sequential)]
        struct HARDWAREINPUT
        {
            public int uMsg;
            public short wParamL;
            public short wParamH;
        }

        //________________________________________________________________________________________
        // Input Region End


        // #############################################################################
        // MOUSE INPUT 
        // #############################################################################
        public static void ClickLeftMouseButton() // left click
        {
            INPUT mouseDownInput = new INPUT();
            mouseDownInput.type = SendInputEventType.MOUSE;
            mouseDownInput.mkhi.mi.dwFlags = MouseEventFlags.MOUSEEVENTF_LEFTDOWN;
            SendInput(1, ref mouseDownInput, Marshal.SizeOf(new INPUT()));

            /*
             * NOTE***
             * Since I have now gotten to this point, I have not done a mouse move yet, but I  believe you
             * might need to your movement to dx,dy like so:
             */
            mouseDownInput.mkhi.mi.dx -= 50;
            mouseDownInput.mkhi.mi.dy -= 80;
            /*
             * ...or apply it's coordinates to the mouse, like this
             */
            //mouseDownInput.mkhi.mi.dx = Cursor.Position.X;
            //mouseDownInput.mkhi.mi.dy = Cursor.Position.Y;

            Console.WriteLine(mouseDownInput.mkhi.mi.dx + "," + mouseDownInput.mkhi.mi.dy +
                " | " + mouseDownInput.mkhi.mi.mouseData + " | " + mouseDownInput.mkhi.mi.time);

            INPUT mouseUpInput = new INPUT();
            mouseUpInput.type = SendInputEventType.MOUSE;
            mouseUpInput.mkhi.mi.dwFlags = MouseEventFlags.MOUSEEVENTF_LEFTUP;
            SendInput(1, ref mouseUpInput, Marshal.SizeOf(new INPUT()));
        }

        public static void ClickRightMouseButton() // right click
        {
            INPUT mouseDownInput = new INPUT();
            mouseDownInput.type = SendInputEventType.MOUSE;
            mouseDownInput.mkhi.mi.dwFlags = MouseEventFlags.MOUSEEVENTF_RIGHTDOWN;
            SendInput(1, ref mouseDownInput, Marshal.SizeOf(new INPUT()));

            INPUT mouseUpInput = new INPUT();
            mouseUpInput.type = SendInputEventType.MOUSE;
            mouseUpInput.mkhi.mi.dwFlags = MouseEventFlags.MOUSEEVENTF_RIGHTUP;
            SendInput(1, ref mouseUpInput, Marshal.SizeOf(new INPUT()));
        }

        /// <summary>
        /// checks for the currently active window then simulates a mouseclick
        /// </summary>
        /// <param name="button">which button to press (left middle up)</param>
        /// <param name="windowName">the window to send to</param>
        public static void MouseClick(string button, string windowName)
        {
            switch (button)
            {
                case "left":
                    mouse_event((uint)MouseEventFlags.MOUSEEVENTF_LEFTDOWN, 0, 0, 0, 0);
                    mouse_event((uint)MouseEventFlags.MOUSEEVENTF_LEFTUP, 0, 0, 0, 0);
                    break;
                case "right":
                    mouse_event((uint)MouseEventFlags.MOUSEEVENTF_RIGHTDOWN, 0, 0, 0, 0);
                    mouse_event((uint)MouseEventFlags.MOUSEEVENTF_RIGHTUP, 0, 0, 0, 0);
                    break;
                case "middle":
                    mouse_event((uint)MouseEventFlags.MOUSEEVENTF_MIDDLEDOWN, 0, 0, 0, 0);
                    mouse_event((uint)MouseEventFlags.MOUSEEVENTF_MIDDLEUP, 0, 0, 0, 0);
                    break;
            }
        }

        // #############################################################################
        // OTHER
        // #############################################################################
        /// <summary>
        /// moves a window and resizes it accordingly
        /// </summary>
        /// <param name="x">x position to move to</param>
        /// <param name="y">y position to move to</param>
        /// <param name="windowName">the window to move</param>
        /// <param name="width">the window's new width</param>
        /// <param name="height">the window's new height</param>
        public static void WindowMove(int x, int y, string windowName, int width, int height)
        {
            IntPtr window = FindWindow(null, windowName);
            if (window != IntPtr.Zero) { MoveWindow(window, x, y, width, height, true); }
        }

        ///// <summary>
        ///// moves a window to a specified position
        ///// </summary>
        ///// <param name="x">x position</param>
        ///// <param name="y">y position</param>
        ///// <param name="windowName">the window to be moved</param>
        //public static void WindowMove(int x, int y, string windowName)
        //{
        //    WindowMove(x, y, windowName, 800, 600);
        //}

        public static void LeftClick(int x, int y)
        {
            Cursor.Position = new System.Drawing.Point(x, y);
            mouse_event((int)(MouseEventFlags.MOUSEEVENTF_LEFTDOWN), x, y, 0, 0);
            mouse_event((int)(MouseEventFlags.MOUSEEVENTF_LEFTUP), x, y, 0, 0);
        }

        private void button1_Click(object sender, EventArgs e)
        {
            posx = 200; posy = 200;
            curx = 100; cury = 100;
            WindowMove(posx, posy, "Form1", 400, 400);
            locx += posx; locy += posy;
            Console.WriteLine(locx + "," + locy);
            SetCursorPos(locx + curx, locy + cury);
            MouseAction("left", "Form1");
            int count = 0; bool rmove = true; 
            int winMaxX = locx + this.Width;
            int winMinX = locx;
            Console.WriteLine("size: " + winMinX + "," + winMaxX);
            do
            {
                SetCursorPos(locx, locy);
                if (locx < winMaxX - 10 && rmove) { locx += 1; Thread.Sleep(1); }
                else 
                {
                    rmove = false; //count += 1; locx -= 1;
                    if (locx > winMinX + 10 && !rmove) { locx -= 1; Thread.Sleep(1); }
                    else { rmove = true; count += 1; }
                    SetCursorPos(locx, locy);
                }

                //Cursor.Position = new Point(locx, locy);
            }
            while (count < 5);
            //LeftClick(350, 150); // your function
            MouseAction("right", "Form1");
        }
    }
}

If you want to manipulate a window, there is some info in Microsoft's Docs. https://msdn.microsoft.com/en-us/library/windows/desktop/ff468919(v=vs.85).aspx This might also be helpful hopefully. http://www.codeproject.com/Tips/825946/Csharp-VB-NET-and-WinAPI-How-to-Access-Window-of-O