Originally Posted by paypal

You can get a hint whether if your site is banned by querying your site in the Google webmasters tool:
Google Webmaster Central

If your site is banned from the Google index, under the "Index Status", it would state "Pages from your site are not included in Google's index.". This holds true if your site was once indexed in Google.

Fortunately, even if your site is banned (from the index), you can request for re-inclusion once you find anything that violates the Google site guidelines (you may need to find out what violated it on your own, as Google doesn't tell you specifically). Google would re-include your site after a short period of time.