DIAGNOSIS The HDMI-CEC handshake between your TV and the Beam has fallen out of sync. The TV isn't sending audio to the correct output, or the Beam's TV audio input got deselected.
FIX Unplug both the Beam and your TV from power for two full minutes. This clears the capacitors and resets the HDMI-CEC brain on both devices. Plug the TV back in first, let it boot, then plug in the Beam. Wait for it to chime and show a solid white light. This almost always re-establishes the connection.
IF THAT DIDN'T WORK Go into your TV's sound settings and manually cycle the audio output. Turn off CEC (often called Simplink, Anynet+, Bravia Sync, etc.), set audio to TV speakers, then turn it back on and select HDMI/ARC again. Sometimes you have to manually select the Beam as the audio device in the TV menu.
HEADS UP If your TV is older and only has optical audio out, the little HDMI-to-optical dongle that comes with the Beam can fail. Try wiggling the optical cable at both ends—if sound crackles back, you need a new cable or dongle.