You’re obviously getting data returned for $attachments = get_posts(); otherwise, you wouldn’t be able to output $attachment->post_title. So the issue must be with your wp_get_attachment_image() call.
The first thing I would check is: why are you setting the $icon parameter to true? This parameter is intended to output a mime-type icon, instead of the actual attachment image. Try setting it to false (or omitting the parameter altogether, since false is the default).
Other than that, it’s a long-shot, but try omitting full, and let wp_get_attachment_image() attempt to output its default image size, thumbnail.