Diagnosis
The soundbar is stuck in a standby or Bluetooth pairing mode. This is usually a temporary software or input glitch.
How to Fix It
Force a reboot. Unplug the soundbar from power for a full 60 seconds, then plug it back in. Wait for it to fully boot (lights will cycle). Use the Bose Music app or your TV remote to select the correct input (like TV or HDMI eARC).
If That Didn't Work
The issue might be the HDMI-CEC handshake with your TV. Turn off your TV, unplug both the TV and soundbar from power for 2 minutes. Plug the TV in first, turn it on, then plug in the soundbar.
Heads Up
A solid white light can also mean it's in Bluetooth pairing mode. If you hear a prompt tone but no audio, press the Bluetooth button on the remote or top panel to exit it.