"Now it doesn't turn on at all."
If it doesn't even boot into a bootloader then that's a hardware issue, contact google (store.google.com/repair if I am not mistaken)
Overall sounds like your phones hardware started to fail after the update. I had this happen before. My 5A one day just told me my OS signature was invalid and would not respond to fastboot commands. Google told me it was a battery issue and they upgraded it for me.
Its somewhat common...ish, when the phone starts to fail it will do things like failing to boot or requesting a data wipe more and more until it eventually dies completely.
Google is fairly good in handling these issues, at least in my experience in the US. They didn't even care I was using GOS, they still paid for the upgrade.