I just rebooted one of my five nanoes and having the no-boot problem. I tried swapping a known good SD card without any luck. I did have a snazzy little SSD1306 display attached to the SCL and SDA pins.
I had the window manager disabled and started it back up again, confirmed it was working and rebooted. Now no boot. I tried closing jumper J40 briefly with no change. No network, nothing.