在ASP.NET中如何将事务放在两个方法中处理？

请教高手：一个页面中有两个按钮，一个按钮用来读取数据并绑定到控件，开始事务，数据修改后，点击第二按钮后提交事务，保存修改。这两个按钮事件如何写？
以下是我写的方法，但不能实现，该如何修改？
    SqlConnection con = DB.dbcon();
    SqlTransaction tran=null;
    protected void Button1_Click(object sender, EventArgs e)
    {
        if (Page.IsValid)
        {
            yuejuantimu();
        }
    }
    public void yuejuantimu()
    {  
        string cmdsql = "select top 5 答案ID,t.科目,内容,考生答案,空后内容,参考答案,分值 from 答案评卷 d ";
        cmdsql += " WITH (updlock,readpast) inner join 试题库 t on t.试题ID=d.试题ID where t.科目= '";
        cmdsql += Request.QueryString["rjxk"].ToString()+ "' and t.题型='";
        cmdsql += DropDownList1.SelectedValue +"' and 小题得分 is null ORDER BY 答案ID ";
        SqlCommand cmd = new SqlCommand(cmdsql, con);
        SqlDataAdapter dpt = new SqlDataAdapter(cmd);
        try
        {
            con.Open();
            tran = con.BeginTransaction(IsolationLevel.RepeatableRead);
            cmd.Transaction = tran;                                    
            DataTable dt = new DataTable();
            dpt.Fill(dt);
            DataList1.DataSource = dt;
            DataList1.DataBind();
            Button1.Enabled = false;
        }
        catch
        {
            tran.Rollback();
            con.Close();
        }
    }

    protected void Button2_Click(object sender, EventArgs e)
    {
        string upstr = "";
        foreach (DataListItem list in DataList1.Items)
        {
            Label lbl = (Label)list.FindControl("lblID");
            TextBox txtda = (TextBox)list.FindControl("txtDaan");
            upstr += " update 答案评卷 set 小题得分=" + txtda.Text + " where 答案ID=" + lbl.Text ;
        }
        con.Open();
        SqlCommand cmd = new SqlCommand(upstr, con);
        tran = con.BeginTransaction(IsolationLevel.RepeatableRead);
        cmd.Transaction = tran;
        cmd.ExecuteNonQuery();   //执行到这里出现 ：超时时间已到。在操作完成之前超时时间已过或服务器未响应。
        ();
        con.Close();
    }
请不吝敕教！