Around September our PageRank on Google was 5, then in October it suddenly dropped to 2. We knew it was strange, but possible. Today our PageRank is zero!!!
Google is penalizing Sampa for something that we didn't do. We never used any tricks or black-hat SEO techniques.
However, Sampa is like a web-hosting company, where we have thousands of websites on the same IP address. All these websites point back to Sampa.com as well. That can be easily perceived as a link farm by Google and other search engines, but it is not.
Now we are not sure how to contact Google about that. Does anyone has any idea how to fix that?
Looks like you're back to 3 now? Google has a well-known "sandbox" effect. They sometimes categorize a new site differently before they put it into the mainstream algorithm. Perhaps you just came out of the sandbox.