Same happened to me recently to a new-to-me preowned active subwoofer for one of my lesser systems. Everything was fine …purchased from a dealer and then suddenly …,, won’t start up.
After the preliminary checks without apparent cause, it was pro tech evaluation time.
RESULT: Poor motherboard design with the caps positioned tooclose to the power supply …. It was creating a surplus of heat . Over time, the accumulated heat exposure dried out the caps and the capacitors were now in tipping over into failure mode and the internal amp would not start out of standby mode …..and voila …,,new capacitors needed to be soldered in.
TAKEAWAY: it could one or more various issues discussed in this thread .. go figger.
