DIAGNOSIS Main power board failure or a blown internal fuse. This is common on units with a direct power surge or a bad power supply.
FIX Unplug the TV from the wall for 60 seconds. Plug it back in directly to a wall outlet, not a power strip. Press and hold the physical power button on the TV itself for 30 seconds. Release and try the remote.
IF THAT DIDN'T WORK The fuse on the main board is blown. This requires a replacement main power board (part number 2494A0832G for most 55U8K units). A technician must install it.
HEADS UP Do not repeatedly try to power it on if it's completely dead. It can damage the panel driver boards. Check your wall outlet with a lamp first.