I just ran into this.
I found an article that said - hold down the power and volume down buttons for 10 seconds to reset but that seemed to do nothing.
So I decided to try every combo of power and button to see if any of it helped. I held down power and volume up for over 10 seconds while plugged into a known good power source and cord - that is when the charging lights came on. The charging lights are now blinking. I turned it on and it still remembers the bluetooth connections.
That was my first guess - so if that doesn't work I'd try holding down other combos of power and other buttons for over 10 seconds to see if it will come back. I would also recommend doing that connected to a known good power source.