bro,
it may be the battery problem only.
happened to me like this(blinking LED) for my galaxy note 2.
when i was visited service center(Amalapuram), they did many things and after 3 days gave to me(all data vanished) and declared battery problem and battery not available at their SCS. Then I purchased a original battery from hyderabad, mobile was started working without any further problem for 2 years.
surely it is not Board problem, mostly once board damaged(Sudden Death syndrome) it won't work again. even LED will not work.
Just asking to consider the battery issues...