Diagnosis
HDMI-CEC handshake failure. The communication protocol between the TV and soundbar has locked up, often due to a power state change or a connected third device disrupting the chain.
How to Fix It
Perform a full HDMI reset. Power off both the TV and soundbar. Disconnect both ends of the HDMI cable. Unplug both devices from wall power for 3 minutes. Reconnect power to both. Reconnect the HDMI cable firmly between the TV's ARC port (usually HDMI 1) and the soundbar's HDMI OUT (TV ARC) port. Power on the TV first, then the soundbar.
If That Didn't Work
Disable and re-enable HDMI-CEC on both devices. On your TV, find the CEC settings (often called Simplink, Anynet+, or BRAVIA Sync). Turn it off, wait 10 seconds, then turn it back on. On the soundbar, ensure 'TV ARC' is selected as the source.
Heads Up
The S40Q supports HDMI ARC but not HDMI eARC. Ensure your TV's audio output is set to 'ARC', not 'eARC', as an eARC setting will cause a handshake failure and no audio.