Error with Arduino Nano

Hello,

I bought several Arduino nano cards shipped from China and, when I plugged it on my Mac, the serial USB port disappear (dev/cu.usbmodem.1411). I thought they are bad quality. I bought new one on eBay from France but the problem is exactly the same: Arduino software doesn't recognise the card. It works well with several Arduino Uno boards.

Can you help me to find what's wrong?

Many thanks, Virgil

Problem solved: https://arduino.stackexchange.com/questions/34775/arduino-nano-not-visible-in-serial-ports-mac-os !!!!

Thank you