A06 and A04 won't boot

I don’t know about the A04, but for the A06, the first boot is insanely slow. Give it several minutes. It won’t be too slow after the first time, but the first one is really slow.

If that doesn’t work, you can try connecting to the serial console (check the micro USB port under where the printer is mounted), but you might have to clip a couple of resistors off the board to get it to work properly.