Sounds like the symptoms I had earlier in the thread. The only way I could get the TV back into operation was to set the Roku OS up without an Internet connection (if you can get the OS to boot up, that is... select No Internet Connection on the first setup screen), and use an HDMI streaming device for streaming stick in an HDMI port for getting to the streaming apps.
The only other known fix, if you are out of warranty, is the hunt down a system board on eBay and replace it yourself - which doesn't look too hard to do actually.
My theory is that what is/was happening is that the storage area of the system board is getting corrupt or failing and causing the Roku OS to think there's a valid upgrade file downloaded to the board that it then tries to upgrade to. When that upgrade fails, it simply defaults back to a default state, reboots, and then finds the corrupt upgrade file again and tries to upgrade again, etc etc etc. over and over and over. A bad design there for sure (both with the **bleep** system board and the OS not allowing for operation without insisting on an upgrade if it finds one.)
