This chassis has a high failure rate of the capacitors on the power supply that cause this very problem.
Samsung is aware of the problem, however have not acted on it.
They mounted the capacitors horizontally on this board - and glued then together - so air does not circulate around them to keep them cool.
This is usually always a Power Supply or a short in the System that causes the Relay to click continuously trying to power the set back up. I see that this is a 55" LED TV. Is this Samsung still under warranty?
If it is, we can't continue forward as it will void the warranty. This is hardware related and being a 55 in, Samsung will have a tech come out to your house and perform the repairs for you.
If it is not under warranty (and may not be anyway since you have already removed the back) the first thing to look at is to check for puffy and/or leaking Capacitors on the Power Supply.
This is a clear indicator of heat stress, and you have 2 options.
Replace the board with a used one (ShopJimmy.com or eBay are good sources) - or take the board in and have the capacitors replaced with better quality/higher rated ones to a void future failure.
In either case - expect to pay about $130 to get it back in running order.
Be sure to match board numbers if you decide to order a replacement yourself. There are more than one version of the board used in this model.
If you have additional - Just Ask.