private int? CheckUserPass()
        {
            // take text boxes
            // user and pass
            // go into db
            // get matching userid


            var matchedUser = from userRow
                in dc.Users
                where userRow.UserName == txtUsername.Text &&
                userRow.Password == txtPassword.Text
                select userRow.UserID;

            if (matchedUser.Any())
                return matchedUser.Single();
            else
            {
                MessageBox.Show("Invalid user or pass");
                // focus clear etc

                return null;
            }

        }