关于一个C#的问题

我用的时access2007数据库，为什么我做的操作不能更新到数据库中去，求指点。
代码：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 System.Data.OleDb;namespace 学生信息档案管理系统
{
    public partial class ScoreUpdate : Form
    {
        OleDbConnection connection = new OleDbConnection(help.connstr);
        OleDbCommand cmd;
        OleDbDataAdapter da;
        OleDbCommandBuilder cb;
        DataSet ds = new DataSet();
        BindingSource bind = new BindingSource();
        public ScoreUpdate()
        {
            InitializeComponent();
        }        private void ScoreUpdate_Load(object sender, EventArgs e)
        {
            bind.DataSource = Getdt();
            this.bindingNavigator1.BindingSource = bind;
            this.dataGridView1.DataSource = bind;
        }
        public DataTable Getdt()
        {
            cmd = new OleDbCommand("select U_Account,U_Pass from User_Login", connection);
            da = new OleDbDataAdapter(cmd);
            da.Fill(ds);
            return ds.Tables[0];
        }        private void button1_Click(object sender, EventArgs e)
        {
            cmd = new OleDbCommand("select U_Account,U_Pass from User_Login", connection);
            da = new OleDbDataAdapter(cmd);
            cb = new OleDbCommandBuilder(da);
            da.InsertCommand = cb.GetInsertCommand();
            da.DeleteCommand = cb.GetDeleteCommand();
            da.UpdateCommand = cb.GetUpdateCommand();
            bind.EndEdit();//提交未更改，应用于数据
            da.Update(ds);
            MessageBox.Show("操作成功");
            ds.Clear();
            bind.DataSource = Getdt();
            this.bindingNavigator1.BindingSource = bind;
            bind.MoveLast();//绑定到最后一条数据
        }
    }
}