Thanks for your reply Robert,
When I try to boot on the sd card, I have the four led that turn on and a I get a black screen on the monitor. That probably means that the sd card I prepared is not bootable
I will try to boot on an image found there BeagleBoard.org - latest-images first.
Afterwards, I will check what could have gone wrong when I followed: Debian: Getting Started with the BeagleBone Black