Diagnosis
Complete power failure. The external power supply unit (PSU) is the most likely point of failure.
How to Fix It
Unplug the soundbar. Check the small, rectangular external power brick on the AC cord. Look for damage. Ensure the cord is fully seated in the brick and the soundbar. Try a different, known-working AC outlet directly. Do not use a power strip.
If That Didn't Work
The internal DC power board may have failed. This requires opening the unit. Contact JBL support for service. Do not attempt a board-level repair yourself.
Heads Up
Never use a generic power adapter. It must supply exactly 24V DC. Using the wrong voltage will damage the soundbar permanently.