Just wanted to share my experience. My Bar 48 got locked as well. I managed to release the power button after 3 of 5 lights turning on (slipped the button).
Tried several times to unplug power cord and reconnect the USB and holding the power button again. I could hear something happening but it would not restart.
I formatted the USB drive and downloaded the same files again and unzipped to USB drive. After that the software update worked.