alexandros While it was not responding, the LEDs on the pb2 where both on (a green one blinking and a red constantly on) and the blue on the bela was blinking.
That means Linux is up and running... while the LEDs behave like that, if it doesn't show up on the host it's either down to a bad usb connection or something overloading the system. It's pretty hard to overload 4 cores, but if you run out of RAM, the OS may freeze for a few seconds. Not sure what happens to the lights there, but within 20 seconds or so it should be working again.