Diagnosis
The power supply has failed. This is almost always the AC/DC adapter, not the soundbar itself.
How to Fix It
Unplug the adapter from the wall and the soundbar. Check the adapter's output label. It must say 19V and at least 3.42A. Use a multimeter to test for voltage. If it reads zero or low, the adapter is bad. Replace it with a compatible 19V DC adapter. Center pin positive, 5.5mm x 2.5mm barrel plug.
If That Didn't Work
If a known-good adapter still gives no power, the internal DC power jack on the soundbar may be damaged. The solder joints can crack. This requires opening the unit to inspect and re-solder.
Heads Up
Never use a generic adapter with the wrong voltage or polarity. You will instantly fry the main board. Match the specs exactly.