Have you tried contacting the manufacturers?
12MHZ is a strange frequency for a Nano. Are they made by WAVGAT?
These are made by RobotDyn:http://robotdyn.com/~iiVMG
1) When connecting to ArduinoIDE's Serial monitor using 9600 Baud this is was comes back:*snip*"test pass" if I write an 'a' on the keyboard and 'Fail!' for everything else. Some kind of self-test from facory.
2) When connecting to other working Arduino Micro Pro, I get another COM-port started a short while after pressing reset (maybe 5s) if looking in Device Manager. Think it is called Leonardo or something similar. Don't know if this is way in?
3) When running Nick Gammon's tool via other working Arduino Micro Pro:-snip-// Atmega chip programmer// Author: Nick Gammon// Date: 22nd May 2012// Version: 1.37-snip-
Do you know if the original bootloader is still on there? I ask because you've mentioned trying to upload via ISP and if you've done that you will have overwritten the bootloader.The best way to check is by powering the Nano up and watching the onboard LED. It should blink once.