Impossible to connect my Wifi Network

Dear all 😉

Here is my story... I just bought a new Airport Express (AE) 🙂

I plugged it home (WITHOUT ETHERNET CABLE I want to connect remotely on my Wifi Network) and it perfectly appeared in my Airport Utility sofware (Mac OS 10.9.

I selected "Join existing network" (Fast Web Wifi Network, I live in Milan/Italy - As in NOT to an apple airport wifi based network).

Having tried several times this afternoon, I saw the airport utilities switching networks (from mine to apple AE network factory settings) to configure the AE base-station within network preference but it always ends with a kind of "Unknow error" (without any reference code) + retry button.

As I click the retry button, another "Unknown error occured" appears and then...

The AE simply disappears (airport utility searches and does not find it) ! 😠

The led turns to green and I can't access AE

Unless I make a factory reset 😟

For your info :

1 - I tried to plug an Ethernet cable, it "fried" my wifi connection : I had to reboot the modem and reset my wifi connection on my mac

2 - It has never been recognized by my iPad

3 - It has been recognized by my iphone 2 times and I tried to download the firmware : it never succeeded

Would anyone help me ???? 😢

Many thanks

Christophe