If your website/blog is totally banned in Google search engine because of some unknown reasons you need to signup with Google Webmaster Tools, add your website in your account and verify it.
Here are some of the reasons why your website may have got banned :
- Hidden Links or Text on your web pages. In many websites there are some hidden text or links which may have been added by the webmaster by mistake or else by someone without the owner’s knowledge. This has to be removed as soon as possible.
- Access Issues – Many a times there are some web pages which can get blocked and which wont allow the search engine bots to access them. You can login to the webmaster tools account to find out if any of your website pages are having access issues. Under the overviews page you will be able to find out when was the last time Google access your website and if there are any issues with it. If your website is down or your server is busy there can be crawling errors which would be reported in the webmaster tools account.
- There are many pages which may be accidently blocked by your robots.txt file which are also reported in the webmaster tools account. Visit Tools > Analyze Robots.txt file and find out when your robots.txt file was last accessed by google and if there are any errors in it.
Check out a Detailed Video on this topic here from the Official Google Channel!