It appears that the website is not loading properly, and there have been numerous reports regarding the availability of CertFX. Therefore, I don't think this service is still available and you'll have to pick something else for test practicing.
You can use the following result list to look for something that you might want to try: http://software.informer.com/search/practice+tests
Access the link above and then choose an application from the list based on its popularity, needs and reviews.