welcome to the sandbox, sit back, relax and continue to build links, you will be back in a couple of months time!
What is your URL? You can get much better help here if you provide your URL. Otherwise, people are just stabbing in the dark.
have you got a google webmasters tools account? ...It will tell you if your website is still indexed or banned.
just wait for some time; this same happen with my site also but now my site is back again on lower page, this happpens because of updation in data center
its a normal googlish behavior to get u in top then just throw you under tons of crap, you will only find out the result of ur work in the next serp update