Did you take an look into the domain before you bought it? It's always worth doing a little investigating before you buy... but we learn from out mistakes
If the reason for being banned has been resolved then you can submit a re-inclusion request to Google through Google Webmaster Tools.
i had a domain banned by google after i forgot to renew and picked it up on the drop, six months later after many letters to google they re-indexed the domain, so just keep writing letters to google's webmasters tool.