mouse_event(MOUSEEVENTF_LEFTUP | MOUSEEVENTF_MOVE | MOUSEEVENTF_ABSOLUTE, 0, 0, 0, 0);

 MouseEventFlags
MousMouseEvent
MouseEventFlags
PosX, PosY

mouse_event(MouseEventFlags.ABSOLUTE | MouseEventFlags.MOVE | MouseEventFlags.LEFTDOWN | MouseEventFlags.LEFTUP, PosX, PosY, null, null);

int PosX = ((Cursor.Position.X * 65535) / Screen.PrimaryScreen.Bounds.Width);
int PosY = ((Cursor.Position.Y * 65535) / Screen.PrimaryScreen.Bounds.Height);

mouse_event(MOUSEEVENTF_LEFTDOWN, 0, 1436, 7, 0);

int x = Convert.ToInt16(textBox1.Text);
            int y = Convert.ToInt16(textBox2.Text);

            // Coordenadas del cursor
            Cursor.Position = new Point(x, y);

            mouse_event(MOUSEEVENTF_LEFTDOWN, 0, 0,0 ,0);
            mouse_event(MOUSEEVENTF_LEFTDOWN, 0, 0, 0, 0);

 private const int MOUSEEVENTF_LEFTDOWN = 0x0002;
        private const int MOUSEEVENTF_LEFTUP = 0x0004;