The domains that you add in WHM are still subject to at least 48 hours propagation time. That means, after you point the domain to the correct nameservers, it will take 48 hours to begin to work.
In the meantime, if you wish to access the account before it propagates, you can use the methods outlined here: http://www.smartweb.com.ng/index.php/knowledgebase.php?action=displayarticle&catid=10&id=23
