DIAGNOSIS A corrupted software/firmware update is preventing a normal boot. This is a known issue after a failed or interrupted update.
FIX Perform a forced factory reset. Unplug the TV from power. Press and HOLD the physical power button on the TV itself (not the remote) for 30 seconds. Plug the TV back in while still holding the button. Continue holding for another 30 seconds after plugging in. This should trigger a reset menu on screen. Use the remote to navigate and confirm a full factory reset.
IF THAT DIDN'T WORK The main board may have a hardware fault. As a last-ditch effort, try a manual firmware update via USB from Samsung's support site, but the forced reset usually resolves it.
HEADS UP A factory reset erases all your settings and logged-in accounts. You'll need to set up WiFi and apps again from scratch.