I had something similar before where my Deck was all of a sudden in a bootloop (black screen, fan running) and I couldn‘t get it out of it until the battery had emptied itself, then it worked just fine again.
Let me know if you ever figure out what went wrong with yours, for my curiosity‘s sake
The power button thing would be very disappointing cause it is a vital button that is expected to be pushed a lot… I hope you can figure it out whatever it is.