You are able to log into several Darknet marketplaces only with an alternative URLs, what determines a tricky situation : upcoming buyers and merchants are not allowed to sign up before they will obtain an alternative links from an already signed in shopper.
Search for those at http://deeponionmarkets.com/, it possesses fresh URL to suggested Deepweb markets. You should go to these alternative link to register on the sites.
If there are some problems with an access (links don't work), you should hang around and check for Darknet markets alternative URL. Keep trying, because a several amount of the markets close and open signing up periodically, based on server load.