This is pretty much what the problem was. I had just brought home the used piano and we were trying it out before bed. I plugged in the headset. I walked away. Then a bit later my husband unplugged them to check out the piano. He didn’t notice the adapter for the headset was left in the piano. I didn’t realize the headset had an adapter on it when I plugged it in. So we thought the piano broken. I sent a text to the previous owner the next evening (it was too late that night.). She told me about the adapter. I removed it & the piano is back in service.