There are a number of way to find the backlinks to a site and one of the operators that Google make available is the link: command ( for eg). As others have noted, this command only ever shows a small random sample of the backlinks to a site and never them all. Sometimes that random sample contains no links. It is just the way it is. It is not a sign that Google is broken, or your site is penalized or Google is not counting all your links. To get a more detailed picture of the links to your site, use your Google Webmaster Tools. Ignore what you see in response to the link: command and do not make any conclusions, let alone decisions based on it.