Thank you to everybody for your help!
Riassembled Kobo.
Just tried to reset...
Now there is on the screen the second one with language to choose.
Nothing works...
I cannot "link" my finger with a single language for continuing that factory reset!
I suspect that OS is not working at all (for a mistake of mine when I unwired kobo during an upgrade firmware from my Kobo Desktop pc) and so it's impossible to reset because I cannot enter any menu by my finger. (Sorry for my english)
Well, if I use Kobo local service warranty, I'll have to wait 1 month plus Xmas period... but now warranty not valid as I opened Kobo
What doing?
First of all, thanking you
and then pick up an hammer... I hate this situation. Kobo is beautiful but having a new OS from official Kobo seems a tabu. Just a download page, too difficult?
Stop thinking, Now I'm going to buy a simple but excellent (it was my first Kobo before Aura HD) Kobo Glo.
Please everybody, when upgrading your Kobo don't unwire it!
PS. Kobo mother-board is fantastic, all in one and a simple but fantastic SanDisk!