I gave my Infocrystals article directory into several free directories available in the market and I suddenly found after two weeks my site was in the top position in Google.com for some of the keywords, but now after a month when I type the same keyword the same results are not showing.

I couldn't find my site in the Google results. why this has happened to Infocrystals, Why my site disappeared suddenly from Google results, what went wrong? I need to reinstate the position in Google, How to do it?