This is one of those classics. The initial on/off was it telling you to unplug and get it fixed. At that point repair was pretty cheap (at least around here) but if you keep using it to the point of it won't work, it can be costly.
HOWEVER it is all of 16 months. CALL IN and ask for the one time warranty extension.
Please consider extending the warranty on gear you don't feel like paying for full repair prices.
It all started with the TV randomly turning on and off a few times with only 30 seconds or so between each switch. This would happen 5 or 6 times and then stop. This morning things escalated when the TV did this on/off cycle 20 times or so and I eventually took it as a sign to get off of my butt. Now the TV will not turn on long enough to see the intro picture and it will start the on/off cycle without touching the remote. I tried unplugging the TV for a while and removing the batteries from all remotes but as soon as I plug it back in it starts the cycle all over again without being prompted. I have had this TV since April 2014 (16 months).
Model # UN50F6400AFXZA