QC 35 i won't turn on anymore after software update

Hello. I used my QC 35 I for a few years with my iPhone and MacBook (both via Bluetooth), and today I wanted to connect my headphones to my Windows PC at work via Bluetooth as well.

I first tried pairing it in the Bluetooth settings of the PC, which seemed to work (it paired), but the PC did not recognize it as an audio device. 

I then realized I had to first download the Bose software, which I did. I then downloaded an update for the headphones. After I did that, my headphones switched off and now won't switch back on. It's completely unresponsive.

I've tried resetting it, but this also doesn't make a difference. What should I do?