DIAGNOSIS The firmware update process has frozen. This can happen if the internet connection dropped during an auto-update.
FIX Force a hard reset. Unplug the soundbar from power. Press and hold the Power button on the soundbar itself for 30 seconds while it is unplugged. Release. Plug it back in. It should boot normally.
IF THAT DIDN'T WORK You may need to manually re-initiate the update via the MusicCast app. After the reset, go to the app's device settings and check for firmware updates.
HEADS UP Do not interrupt power during any future updates. Updates are pushed automatically. You cannot disable them.