Thank you for the help.
I succeeded to restart the Home Media HMND2 of my wife which was taking the dust after the latest update I did.
I even managed to recover the data on the disk, but it has been painful : I had to install raid utilities AND lvm utilities on my personal computer ( Linux Mint 18.2 Sonya ) .
I should emphasize on the use of an USB stick WITH activity led.
My first try was with a stick without led and I never succeeded.
I got a new one WITH the led : it worked on the first try.
One more time : Thank you !