I recently made the index page have more of my target key words. My google rankings dropped immediately. Is this because I am being penalized for too many key words, or is it because of something else?

My site is http://www.learn-hindi-online.com

My target key words are:
learn hindi online
learn hindi
hindi

When reading the index page, it seems natural to me. It doesn't seem like its over stuffed or anything like that.

Also if you have other advice, thanks.