MacBook Air - external HDD and USB HUB - don't see the drive

Hi,

forgive me for any stupid thing I will eventually say, I'm a brand new mac user

As you know, I have only one usb port, so I connected an external USB HUB at the port, to connect more devices. At the moment, this hub is a portable 4 port 1.1 USB hub.

I connected the mouse. It works.
I connected the Apple Ethernet adapter. It works.
I connected the external HDD. No, it doesn't work. No evidence of it in System Profiler, nothing mounted. it works perfectly on Windows machines with the same hub.

Can you please help me?

the external hdd has 2 usb cable to have also the power, and then I can't connect it directly to my MB Air.

Thanks in advance,