Some users may find it difficult to add organizations to CircleCI from Github after the point of signup as a new oAuth token must be created with access to the new Org being granted access.
1. Remove all cookies for Circleci.com. You can do this by accessing your Chrome developer tools (right-click the page, and select "inspect") while on any page, navigating to "application" and deleting everything under cookies.
2. Click the "Login" button on the home page will become a "Sign Up" button. At the next screen, you will be asked to Authorize CircleCI, be sure to also select "Grant" next to the Organization you would like to add.
Once logged in you should be able to add projects from the new organization. If you run into any issues, contact support for help.