DateTime dateTimeMin = Convert.ToDateTime("2014-01-01");

            DateTime dateTimeMax = Convert.ToDateTime(System.DateTime.Now );

            TimeSpan ts = new TimeSpan(dateTimeMax.Ticks - dateTimeMin.Ticks);

            Random r = new Random(unchecked((int)DateTime.Now.Ticks));

            DateTime dateRandom = dateTimeMin.AddDays(r.Next(ts.Days + 1));

            Response.Write(dateRandom.ToString("yyyy-MM-dd"));