1. You’ve been outcompeted. The most common reason a site doesn’t rank on the first page is because the competition is playing Google’s algorithm game better. Google’s algorithm is based on site age, URL relevance, and Trustrank. “Trustrank, for those who aren’t SEO geeks, is the actual measure of the level of trust that Google holds for your site, which is largely based on the number, quality, and age of incoming links,” Bailyn explains.
  2. Your site has been sandboxed, or re-sandboxed. “Sandboxing” refers to the ranking freeze that Google places on almost all new websites while it builds up a profile of trust. The sandbox period lasts anywhere from two months to a year, depending on the link patterns a site establishes in its first few months, Bailyn says.A lot of people in the SEO world are familiar with the Sandbox, but most people don’t realize that a site can go right back into the Sandbox if Google perceives that the site cannot be trusted to abide by its quality guidelines anymore.
  3. Your site has been penalized. A penalty is the most sinister thing that can happen to a website because Google does not explain it anywhere, or even acknowledge it in a site’s Webmaster Tools control panel.  This penalty is real, but the number of ranking places a site can be penalized is not so standardized. The reason a site gets knocked off the first page has to do with a sudden change to the links going to the site. Google is cracking down hard on paid links now, so if you were, for instance, to buy a number of paid links and did not include a “nofollow” in the linking code, it is likely Google would penalize your site.
  4. You’ve been banned. While this is the worst thing that can happen to your site, it is also the easiest to spot, Bailyn says. If your site has been banned, Google may e-mail you, or else you will have a notification in your Webmaster Tools control panel. Another clear sign that your site has been banned is that a search for www.yoursite.com in Google brings up no results – in contrast, if your site has been penalized, the same search will bring up your site’s home page. Google only bans sites that are involved in black hat SEO (cloaking, doorway pages) or are linked into “bad neighborhoods” (adult, pills, or gambling).You can always submit a reinclusion request once you’ve cleaned up the mess.