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Hi Margaret and welcome to JustAnswer,Thank you for the question and your patience. Should you still need assistance for information purposes only...Initially, even if the Samsung would be "...switching on & off...", would there still be some indication of power such as a standby light or even a blinking LED light?
Based on the above and if problem persist with any/all sources, it would then appear to be an internal hardware issue or more particularly a low or intermittent internal power supply voltage and/or the Samsung is kicking in auto-protect mode.
The above would require that the unit be opened up for visual inspection, voltage/continuity/resistance checks, confirm faults and effect repairs.
Are you then considering a DIY (do-it-yourself) repair approach? If yes, do you have access to and familiar with a multi-meter and even perhaps a soldering iron?
I understand and if no DIY, options are:
Please post back how you would want to approach this and/or should additional information be needed.
Again I understand Margaret and it would appear to be more to your advantage.
Please click HERE should it be of interest.
Good luck and thank you too for the opportunity to be able to share the information.