ช่วยผมหน่อย ผม วนอยู่แต่ในGridView ทำอะไรต่อไม่ได้เลย

 try
 {
 sb.Remove(0, sb.Length);
 sb.Append("select ou_code,fg_code,old_price,u_price,fg_name from in_goods where fg_code='" + txtid_product.Text + "'");
 string sqlin_goods = sb.ToString();
 SqlDataReader dr;
  DataTable dt;
  com = new SqlCommand(); {
  com.CommandType = CommandType.Text;
  com.CommandText = sqlin_goods;
  com.Connection = con;
  dr = com.ExecuteReader();
   if (dr.HasRows)
      {
          dt = new DataTable();
          dt.Load(dr);
          lb_Ou_code.Text = dt.Rows[0]["ou_code"].ToString();
          lb_fg_code.Text = dt.Rows[0]["fg_code"].ToString();
          lb_old_price.Text = dt.Rows[0]["old_price"].ToString();
          txt_u_price.Text = dt.Rows[0]["u_price"].ToString();
          lb_fg_name.Text = dt.Rows[0]["fg_name"].ToString();
          txtid_product.Text = "";

         Calculate();          

                    }
                    else
                    {
                        fmshowdata fms = new fmshowdata();
                        fms.ShowDialog();
                        txtid_product .Text  = fms.getID;                                              
                        
                    } dr.Close();
                                  
                }

                   }catch (Exception ex){

                       MessageBox.Show("จุดเกิดข้อผิดผลาด"+ex, "รายงานความผิดผลาด", MessageBoxButtons.OK, MessageBoxIcon.Error);
                       return;
                  
                   }