Well after 3 days of headsmahsing against this issue and trying to resolve it by reading the documentation available, I think it’s time to expose my problem. ^^
Every time I try to create a new web site from acquia dev top, at the database configuration step, it doesn’t set up the database at all and give me directly “Drupal is already installed”.
When I try to view my “existing site”, I have “The website encountered an unexpected error. Please try again later”.
This problem occur with every version of drupal, and every version of php I try to install. Trust me I try every combination, and of course I have try the right configuration first, as describe here: https://www.drupal.org/requirements.
Of course, I have also tried what is indicated: • “To start over, you must empty your existing database and copy default.settings.php over settings.php.”
I have delete the previous database, and copy default.settings.php over settings.php. But it’s just bug and give me :
Échec de connexion à votre serveur de base de données. Le serveur retourne le message suivant : SQLSTATE[HY000]  php_network_getaddresses: getaddrinfo failed: H�te inconnu. .
I also try to desinstall and reinstall acquia dev top (with the last version up to date). Every dev desktop folders and files have full authorization.
It’s really weird, because 3 days ago, I created and installed a local web site with drupal 8 with acquia dev top. It worked perfectly fine, until I mess up by installing a wrong theme (^^). After that, every time I try to create a new site, I obtain the result as described before.
My last guess is that the problem is inside Phpmyadmin. Anyone have a suggestion ? ^^
I am running out of option, and I think I will turn to another solution than Acquia Dev top.
Thanks for your attention and consideration.