C# MySQL + Login รบกวนพี่ๆดูโค้ดนี่หน่อยครับ ไม่ทราบว่าผมทำผิดตรงไหน พอดีมือใหม่หัดเขียนครับ

using System;
using System.Collections.Generic;
using System.Text;
using System.Windows.Forms;
using System.Diagnostics;
using System.IO;
using MySql.Data.MySqlClient;

namespace LoginFormCS
{
    class dbconnect
    {   
        private MySqlConnection connection;
        private string server;
        private string database;
        private string uid;
        private string password;
        //Constructor
        public dbconnect()
        {
            Initialize();
        }
        //Initialize values
        private void Initialize()
        {
            server = "localhost";
            database = "supplies";
            uid = "root";
            password = "12345678";
            string connectionString;
            connectionString = "SERVER=" + server + ";" + "DATABASE=" + database + ";" + "UID=" + uid + ";" + "PASSWORD=" + password + ";";

            connection = new MySqlConnection(connectionString);
        }
        //open connection to database
        private bool OpenConnection()
        {
            try
            {
                connection.Open();
                return true;
            }
            catch (MySqlException ex)
            {
                //When handling errors, you can your application's response based on the error number.
                //The two most common error numbers when connecting are as follows:
                //0: Cannot connect to server.
                //1045: Invalid user name and/or password.
                switch (ex.Number)
                {
                    case 0:
                        MessageBox.Show("Cannot connect to server.  Contact administrator");
                        break;

                    case 1045:
                        MessageBox.Show("Invalid username/password, please try again");
                        break;
                }
                return false;
            }
        }

        //Close connection
        private bool CloseConnection()
        {
            try
            {
                connection.Close();
                return true;
            }
            catch (MySqlException ex)
            {
                MessageBox.Show(ex.Message);
                return false;
            }
        }

    }//class
}

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 MySql.Data.MySqlClient;
using System.IO;
namespace LoginFormCS
{
    public partial class frmLogin : Form
    {
        private dbconnect DBConn;
        public frmLogin()
        {
            InitializeComponent();
            DBConn = new dbconnect();
        }
      

        private void btnLogin_Click(object sender, EventArgs e)
        {
            
            string strSQL = null;
            int intNumRows = 0;
            strSQL = "SELECT COUNT(*) FROM tbl_user WHERE user_name = '" + this.txtUsername.Text + "' AND user_pass = '" + this.txtPassword.Text + "' ";
             
            DBConn.ToString();  
            //ตั้งแต่บรรทัดนี้  เป็นต่อไป  เิกิด Error
            MySqlCommand objCmd = new MySqlCommand(strSQL,___);
            

            intNumRows = Convert.ToInt32(objCmd.ExecuteScalar());
            if (intNumRows > 0)
            {
                frmMain frm = new frmMain();
                frm._strUser = this.txtUsername.Text;
                frm.LoadInfor();
                frm.Show();
                this.Hide();
            }
            else
            {
                MessageBox.Show("Username or Password Incorrect");
            } 
           
        }
        private void btnClose_Click(object sender, EventArgs e)
        {
            if (MessageBox.Show("Are you sure to exit?", "Confirm.", MessageBoxButtons.YesNo,MessageBoxIcon.Question,MessageBoxDefaultButton.Button1) == DialogResult.Yes)
            {
                Application.Exit();
            }
        }

        private void frmLogin_Load(object sender, EventArgs e)
        {

        }
    }
}