Have you ever wonder why Google banned your site or know someone's site that got banned ? I know that I have.
That is one thing I hate about Google they do not give you any explanation on why they banned your site.
You would think that they would tell you something,so that you may fix the mistake, but they don't.
I currently have a site under review by Google, so that they will index my site in Google.
Hopefully my site will get index

Google rarely bans websites, however those who are banned are either exploiting something, providing illegal content, spamming or websites that appear to be link farms or "phishing" sites. Unfortunately I can't tell you what has happened exactly in your case as I don't know the type of website you have, but I would be careful next time and obtain a clear response from Google. Also, many Webmasters say they were banned when they weren't, so make sure you are first.