Get and retrive data using n-tire asp.net

Question

hi everybody i have made n tire to  make insert , update , select and delete

insert and delete works fine but i have  problem to make select all data in order to make update

this is a method in db.class where connection can be perform

 public void ConnectDB(CommandType CT,string ProNameSQl)
    {
        cn = new SqlConnection("Data Source=.;Initial Catalog=Conversation;Integrated Security=True");
        cmd = new SqlCommand();

        cmd.Connection = cn;
        cmd.CommandType = CT;
        cmd.CommandText = ProNameSQl;
        cn.Open();
    }
 
    public int RunProcedure(string ProcedureName, SortedList Paraval)
    {
        ConnectDB(CommandType.StoredProcedure, ProcedureName);

        for (int x = 0; x < Paraval.Count; x++)
        {
            try
            {

                cmd.Parameters.AddWithValue(Paraval.GetKey(x).ToString(), Paraval.GetByIndex(x));
            }
            catch
            {
                ;
            }
        }
        return ExceNoneQuery();
    }
 public DataTable RunSQl(string Select)
    {
        ConnectDB(CommandType.Text, Select);

        dt=new DataTable();
        dt.Load(cmd.ExecuteReader());
        cn.Close();
        return dt;
    }

 
and then after check i make another class to pass the type of operation  "i" refers to procdure name in sql

  public bool Add()
     {
         return LoadProperties2List("i");
     }

if every thing ok it runs to the last tire where the code can perform like insert 

public class UsersInfo :MainTable
{
    #region Feild
    private string _id;
    private string _username;
    private string _SecondarySchool;
    private string _University;
  
    #endregion

    #region Properties

    public string id
    {
        get
        {
            return _id;
        }
        set
        {
            _id = value;
        }
    }

    public string UserName
    {
        get
        {
            return _username;
        }
        set
        {
            _username = value;
        }
    }

    public string SecondarySchool
    {
        get
        {
            return _SecondarySchool;
        }
        set
        {
            _SecondarySchool = value;
        }
    }

    public string University
    {
        get
        {
            return _University;
        }
        set
        {
            _University = value;
        }
    }

  

  
    #endregion

    public override bool LoadProperties2List(string TypeOfOperation)
    {
        SortedList Sl = new SortedList();
       
        Sl.Add("@CommandType", TypeOfOperation);
        Sl.Add("@UserName",UserName);
        Sl.Add("@SecondarySchool",SecondarySchool);
        Sl.Add("@University",University);
       

        ProcedureName = "MangeUserInfo";
        if (db.RunProcedure(ProcedureName, Sl) == 1)
            return true;
        else
            return false;

    }

    public bool Register(string User, string SecondaryS, string Unvi)
    {
        this.UserName = User;
        this.SecondarySchool = SecondaryS;
        this.University = Unvi;
      

        if (Add())
            return true;
        else
            return false;
    }

this code works fine how to use these layers to sellect and retrive database and show them in textboxes ???  using the same layers