I just reported, discussed and actually solved an issue in your forums:
Piwik detected the MYSQLI adapter on my server, which seems not to work after the setup. I had to manually set it to "PDO_MYSQL" to get piwik working at all.
It might be a little issue, but someone who has not the patience to investigate on this might come to the result that piwik doesn't work at all, easily and give up.
Thanks. The problem with MYSQLI+libmysqlclient is fixed in . Marking as a duplicate of #2341.