Arduino Nano v3 all LEDS on and not detected in Arduino IDE


I previously had a perfectly working Nano and then i connected it to a PCB which i had soldered with components according to a schematic with stepper motor drivers and sensor. The Nano suddenly stopped working and both stepper motor drivers A4988 are no longer working. I used a 9 V DC battery supply. I guess the motor drivers are toast? I unplugged the Nano from the PCB and connected it to the USB cable to see if there was any change but the LEDs stay on. And the Nano is not being detected at any COM port in Arduino IDE. Can my Nano still be rescued or is it done for? :frowning:

I just tried with a second Nano and it's now exhibiting the same symptoms. I guess i just killed two of them. :o

Is the Nano protected against reverse voltage to the Vin pin?