Contact your hosting provider and show them the error on this page:
http://www.pensionpourchiens-saintpardoux.com/powergallery/galleries/slideshow_dissolve/index.php?gallery=1&theme=dark
The important part of the error is:
Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock'
This is a server configuration issue your hosting provider should be able to fix for you.