It's a penalty, same thing happened with my site with building too much links fast. It will come back pretty soon, mine was penalized for 1 month, and was nowhere to be found in first 1000 for a keyword with 0 competition, now just a couple of days ago it suddenly appeared on page 5-6-7 for literary all the keywords and slowly going up. Don't build links, only fresh content and some social bookmarks as they are the new hype for google.