Linq to Sql, problème de maj avec paramètre

public void UpdateData(Guid id, string nom)
        {
            DataContext context = new DataContext();
            Data d = context.Data.DataById(id);
            //d.NOM="changement_qui_marche";
            d.NOM = nom;
            context.SubmitChanges();
        }

       var context = new WpfApplication1.DataContextDataContext();
            var c = (from contact in context.Contacts
                    where contact.ContactID == 1
                    select contact).Single() ;
            c.FirstName = c.FirstName + "!!!";
            context.SubmitChanges();