Although I do not have a solution for your issue, I can say that your next best coarse of action would be to contact the Samsung service center in your region.
It starts happening last week. The first couple of days, the TV will turn on after 3-5mins after I pressed "ON" button. But it's getting worst. Now, after I pressed "ON" button, it will try to turn on the TV, but then it turns itself off, and wait for like 30 sec, it tries to turn itself on again, then off again... for about an hour, then it stays "ON".