This issue has been bothering me for few years, now it can be easily fixed. Manty thanks rd013 and Stephen Stragnell for your great contributions to the community.
As rd013 pointed out, the problem was related to the firmware upgrade and wifi password loss.
I followed the instructions from Stephen: remove the back cover, and unplug and replug the circuit boards, and anything that has a plug, and blow the dust out of the connections. The firmware went back to its original version after those steps and the tv could stay on. I then turned off the auto upgrade and blocked www.samsungotn.net from the router.