Whatever may be the reason, sometime your site get banned or penalized by Google.You know your site is crystal clean and have not used any black hat SEO technique to fool Google, but stillâ€¦â€¦
Donâ€™t get panic, but look for technical reasons the site may not be index or have been penalized
# Look at the robots exclusion protocol and robots exclusion meta tags as both can affect web robots crawling process which is responsible for indexing.
* Robots exclusion protocol is a method that allows Web site administrators to indicate to visiting robots which parts of their site should not be visited by the robot.
* Robots meta tag allows a web master to indicate a robot whether a page may or may not be indexed, or analyzed for links, through the use of a special HTML META tag.
# Check whether 301 redirects are properly implemented:
The 301 redirect is like a change-of-address card for a URL. It means a Web page address has permanently moved to a new address. If search engines have limited or no access to the new URLs, Web pages wonâ€™t appear in search results, that means your are not index.
If 301 redirects arenâ€™t properly implemented, they can really mess up a siteâ€™s link development
# Check for Linking :
A Web site owner has no control over how other sites link to his site, but he has complete control over how he links to other sites. Therefore, search engines rarely penalize a site for how other sites link to yours, with the exception of link farms, but modifying all outbound links on a page to have a nofollow attribute, site owners change the hub or authority score of that page. That can have a negative impact on search engine visibility and may be site get penalized.
# Check profile of your affiliate sites :
Sometimes our affiliate sites can use some black-hat SEO techniques to get high PR, such as participating in link farms to achieve instant link popularity, due to which Google can penalized both sites, even though we actually not participated in link farm.