C(#) asp.net修改密码

请教高手指教 怎么修改密码：我用的是Linq 连接数据库，下面是我在修改按钮上写的代码，请教  是在哪里出错  修改不了？
protected void Button1_Click(object sender, EventArgs e)
        {
            if (Session["username"]!=null)
            {
                myUserDataContext context = new myUserDataContext();
                var p = "";
                var q = from o in context.UserInfoTable
                       
                        select new { 
                            p=o.UserPwd
                        };
                if (TextBox1.Text!=p)
                {
                    RequiredFieldValidator1.ErrorMessage = "原始密码不正确！";
                    //Response.Write("<script>alert('原始密码不正确')</script>");
                }
                else
                {
                    myUserDataContext db = new myUserDataContext();
                    UserInfoTable ui = new UserInfoTable();
                    ui.UserPwd = TextBox2.Text;
                    db.UserInfoTable.InsertOnSubmit(ui);
                    db.SubmitChanges();
                    Response.Write("<script>alert('恭喜你修改密码成功')</script>");
                   
                    Response.Redirect("Default.aspx");
                }
            }
            else
            {
                Response.Redirect("UserLogin.aspx");
            }
        }