How to update password and keep the record of current password in another table

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LINQ

Linq2Sql

I am working in dot net with c# and LINQ and SQL server as database
I have three tables s_reg,s_log,s_pass
s_reg has reg_id primary key,s_log has log_id and reg_id as primary and foreign key resp.,s_pass has pass_id and log_id as primary and foreign key
I want to update password of a ID in s_reg and keep the old password in the s_pass table and also update new password in s_log table with reg_id
i have updated password column in s_reg but it is only accepting reg_id(as it is on auto increment) and new password instead of old and showing remaining fields as NULL
also changes are taking place in s_log and s_pass tables but both are not accepting reg_id, the reg_id column is showing either NULL or 0

What I have tried:

protected void Button1_Click(object sender, EventArgs e)
   {
       using (studentDataContext ps = new studentDataContext())
       {


           var check = (from m in ps.s_regs
                        join s in ps.s_logs on m.reg_id equals s.reg_id
                        where s.susnm == TextBox1.Text && s.spass == TextBox2.Text
                        select new { s, m }).FirstOrDefault();
           if (check != null)
           {
               try
               {
                   s_log log = new s_log();
                   using (studentDataContext database = new studentDataContext())//update column
                   {
                       var up = ps.s_regs.Where(a => a.spass == TextBox2.Text).FirstOrDefault();
                       if (up != null)
                       {
                           s_reg reg = new s_reg();
                           reg.spass = TextBox2.Text;
                           ps.s_regs.InsertOnSubmit(reg);
                           ps.SubmitChanges();
                           Response.Write("<script>alert('save successfuly');</script>");
                       }

                       else
                       {
                           up.spass = TextBox3.Text;
                           log.reg_id = reg.reg_id;
                           ps.SubmitChanges();
                           Response.Write("<script>alert('Update successfuly');</script>");
                       }

                   }
                   s_pass ureg = new s_pass();

                   var chk = (from m in ps.s_passes
                              join n in ps.s_regs on m.reg_id equals n.reg_id
                              select new { m.ppass, n.sname }).FirstOrDefault();
                   if (chk != null)
                   {
                       try
                       {

                           ureg.pname = TextBox5.Text;
                           ureg.puname = TextBox1.Text;
                           ureg.ppass = TextBox2.Text;
                           ureg.reg_id = reg.reg_id;
                           ps.s_passes.InsertOnSubmit(ureg);
                           ps.SubmitChanges();
                       }
                       catch (Exception ex)
                       {
                           Response.Write("Error:" + ex.Message);
                       }

                       var query = (from ord in ps.s_logs
                                    join trd in ps.s_regs
                                    on ord.reg_id equals trd.reg_id
                                    where trd.susnm == TextBox1.Text
                                    select new { ord, trd }).FirstOrDefault();
                       if (query != null)
                       {
                           try
                           {
                               log.susnm = TextBox1.Text;
                               log.spass = TextBox3.Text;
                               log.reg_id = reg.reg_id;

                               ps.s_logs.InsertOnSubmit(log);
                               ps.SubmitChanges();
                           }

                           catch (Exception ex)
                           {
                               Response.Write("Error:" + ex.Message);
                           }
                       }
                   }


           else
           {
                   ScriptManager.RegisterStartupScript(Page, Page.GetType(), "str", "alert(' please check user name and password ');", true);
               }

           }
               catch (Exception ex)
               {
                   Response.Write("Error:" + ex.Message);
               }
           }
       }
   }