How old is your site?
I doubt you have been placed back in the sandbox but have been wiped out of the SERPs. This happened because when googlebot may have tried to crawl your site, it found nothing or I may say, the content was totally different that what it had previously indexed. Hopefully you are using Google's webmaster tools, use it to the full extent. Start SEO again and yeah, ask Googe for a reconsideration, but if your content is totally new then i doubt it will help?
Hadn't you taken a database Backup?