提示Connection没有打开

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Data.SqlClient;
using System.Data;

namespace MySchool
{
class DBHelp
{
private string connStr = "Data Source=.;Initial Catalog=SchoolDB;Integrated Security=True";
private SqlConnection connection;
public SqlConnection Connection
{
get
{
connection = new SqlConnection(connStr); ;
return connection;

        }
    }
    public void OpenConnection() 
    {
        if (Connection.State == ConnectionState.Closed)
        {
            Connection.Open();
        }
        else if(Connection.State==ConnectionState.Broken) 
        {
            Connection.Close();
            Connection.Open();
        }
    }
    public void CloseConnection() 
    {
        if(Connection.State==ConnectionState.Open||Connection.State==ConnectionState.Broken)
        {
            Connection.Close();
        }
    }
}

}

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.Data.SqlClient;

namespace MySchool
{
public partial class frmLogin : Form
{
public frmLogin()
{
InitializeComponent();
}
public const string HINT = "提示";

    private void btnLogin_Click(object sender, EventArgs e)
    {
        string name = txtLogin.Text;
        string pwd = txtPwd.Text;
        string type=cmbType.Text;
        if(name.Equals(string.Empty))
        {
            MessageBox.Show("用户名不能为空",HINT,MessageBoxButtons.OK,MessageBoxIcon.Exclamation);
            txtLogin.Focus();
        }
        else if (pwd.Equals(string.Empty))
        {
            MessageBox.Show("密码不能为空",HINT,MessageBoxButtons.OK,MessageBoxIcon.Exclamation);
            txtPwd.Focus();
        }
        else
        {
            //string connStr = "Data Source=.;Initial Catalog=SchoolDB;User ID=sa;Password=1972";
            //SqlConnection connection = new SqlConnection(connStr);
            //connection.Open();
            DBHelp help = new DBHelp();
            help.OpenConnection();
            string sqlStr = "select count(*) from Administracter where UserName='" + name + "' and LoginPwd='" + pwd + "'";
            SqlCommand cmd = new SqlCommand(sqlStr,help.Connection);

            int iRet = (int)cmd.ExecuteScalar();
            if (iRet != 0)
            {
                Teacher tch = new Teacher();
                tch.name = name;
                tch.Show();
                this.Hide();
            }
            else
            {
                MessageBox.Show("用户名密码不匹配", HINT, MessageBoxButtons.OK,MessageBoxIcon.Error);
            }
            help.CloseConnection();
        }

    }

    private void btnCancel_Click(object sender, EventArgs e)
    {
        DialogResult dlg =MessageBox.Show("确定吗","提示",MessageBoxButtons.YesNo,MessageBoxIcon.Question);
        if (dlg == DialogResult.Yes) 
        {
            this.Close();
        }

    }

    private void frmLogin_Load(object sender, EventArgs e)
    {
        cmbType.SelectedIndex = 0;
    }
}

}

这多半是你数据库的配置的问题，看下错误编号，如果是26 40等，可以检查sql server配置