"reaches a low rank in searches"

Emmanuel, you are not the only one affected (not that this is any consolation)
May I suggest to read some of the posts on Webmasterworld, a no-nonsense forum of mainly professional webmasters, where I have been a member for 10 years and followed the rise and decline of several search engines.
Today Google is on the decline and Bing (despite its illustrious brand name, Microsoft) has a very poor performing indexing robot.

Best to start at the current posts : http://www.webmasterworld.com/active.htm
and more if you feel inclined.