I have a Samsung Galaxy S8+ that will not power on unless plugged in and when plugged in powers on automatically and cycles through the boot screen where it says Samsung Galaxy. Just turns on, then off, then on. There was no pysical damage to the phone, no moisture and I'm using the charger that came with the phone. even tried a charger from another S8+ on my account. Samusng provided no help and Verizon directed me here. I installed a new syste, update the night before this began. Been through all of the troubleshooting possibilities I can find.