Can't get Omega Wizard to work, nor getting contact with database

Hi!

I'm fairly new to Drupal and particularly to Drush.

Having the idea to create a subtheme of Omega with Drush, I proceeded to install Drush using these instructions: https://www.youtube.com/watch?v=x3-OlfI3bAI.

I soon became aware that you now need to install Drush using Composer, so I did that. I deleted the previous installation, but want to mention that in case the subsequent problem might have anything to do with that.

Anyway, I just can't get anything to work. When I write "drush help --filter:omega", the software shows all commands (including, in fact, the Omega commands).

When I write "drush omega-wizard", the following error message is given:

The drush command 'omega-wizard' could not be found.  Run `drush     [error]
cache-clear drush` to clear the commandfile cache if you have
installed new extensions.
Drush was not able to start (bootstrap) the Drupal database.         [error]
Hint: This may occur when Drush is trying to:
 * bootstrap a site that has not been installed or does not have a
configured database. In this case you can select another site with a
working database setup by specifying the URI to use with the --uri
parameter on the command line. See `drush topic docs-aliases` for
details.
 * connect the database through a socket. The socket file may be
wrong or the php-cli may have no access to it in a jailed shell. See
http://drupal.org/node/1428638 for details.

I guess that means that Drush cannot connect to the database either (of course, my Drupal installation has no problem doing that).

I am running Drush from the home catalogue of my Drupal installation (it's on a server). I have tried emptying the cache several times. I have tried replacing localhost with 127.0.0.1. The setting.php-file is in the /sites/default catalogue, so no problems there. I have also tried going back to Drush 7.0 without any change.

So what am I doing wrong? Might I be better off uninstalling and reinstalling Drush? Could anyone give me a hint on how to do that?

Thank you! /Andreas