文件的RAR文件！
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C#中代码写的正确，但是F5的时候却说数据库连接失败啊

代码如下：
namespace Link
{
    class DBHelper
    {
      //连接数据库事件
        public static string conString = "Data Source=MICROSOF-237019;Initial Catalog=User;User ID=sa";
        public static SqlConnection openConnection()
        {
            SqlConnection con = null;
            try
            {
                con =new SqlConnection(conString);
                con.Open();
            }
            catch(Exception e)
            {
                MessageBox.Show("连接有误");
            }
            return con;

        }
        public static void closeConnection(SqlConnection con)
        {
            try
            {
               if(con!=null)
               {
                   con.Close();
               }
            }
            catch(Exception e)
            {
                MessageBox.Show("关闭数据库有问题");
            }
        }
    }
}

设计窗体后
using System;
using System.Collections.Generic;
using
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;

namespace Link
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        //登陆的Clicl事件
        private void btnLogin_Click(object sender, EventArgs e)
        {
            string username = this.txtUser.Text;
            string password = this.txtPass.Text;
            string type = this.cmbType.Text;
            switch (type)
            {
                case "学生":
                    UserManager um1 = new UserManager();
                    bool isOk1 = um1.login(username, password);
                    if (isOk1)
                    {
                        MessageBox.Show("登陆成功");

                    }
                    else
                    {
                        MessageBox.Show("登陆失败");
                    }
                    break;
                case "教师":
                    UserManager um2 = new UserManager();
                    bool isOk2 = um2.login(username, password);
                    if (isOk2)
                    {
                        MessageBox.Show("登陆成功");

                    }
                    else
                    {
                        MessageBox.Show("登陆失败");
                    }
                    break;
                default:
                    MessageBox.Show("类型有误");
                    break;
            }
        }
        //退出的事件
        private void bunCanal_Click(object sender, EventArgs e)
        {
            Application.Exit();
        }
    }
}

//运行的程序
namespace Link
{
    static class Program
    {
        /// <summary>
        /// 应用程序的主入口点。
        /// </summary>
        [STAThread]
        static void Main()
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            Application.Run(new Form1());
        }
    }

做的一个简单的登陆系统的
我生成都是成功的哇，没有报错，但是运行结束后就会报错啊，说连接有误啊，是不是我家里的SQL数据库有问题啊，但是我在我朋友家运行好好的啊，请各位高手帮帮忙啊，在这先谢谢啦！