Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
Cases of cyclic restart like that, are definitely a symptom of one of two things:
A. a severe failure of initialization, causing a restart as the only appropriate way of dealing with it, or
B. a shorted component that forces a restart as a protective measure
(more or less)
... or perhaps, both. At least that's what it seems like to me.
I suggest that you seek a voltage that is being held down by a shorted board (or, component on one board). This may be difficult to measure with the constant restarts, but is one way toward a diagnosis.
Also, a service manual, with troubleshooting procedures and details as to voltages to measure here or there within the TV, would help you considerably.
A reliable source for a service manual for your model would be
depending upon whether you want a download or a paper hard-copy version of the service manual.
Another (crude) troubleshooting technique, if you should not bother with getting a manual, would be to unplug one board from the TV, then plug the TV in and power it On, seeing whether that board's removal relieves the problem... but a service manual's information would be much better for the chances of settling this case with reasonable efficiency.