@nellzbear you will need to let us know exactly what you have done. Power cycling is actually an On-off-on cycle which would be indicative off a bad MOSFETs on the main board. Turning on and then off is most commonly related to either a bad power board or a failure of a board to initiate. Remove the back cover from your TV and visually inspect your boards for any damaged looking components. Post some pictures of all of your boards with your question. [guide|21499]
Also, make sure you unplug everything from your TV. Things like sound bar, cable box, Firestick etc. then unplug the TV and hold down the power button for about a minute. After that connect one local video input source (DVD player etc.) and see if that has changed the TV’s behaviour