By default, cPanel is configured to disable a user after a certain number of failed logins. You will see the message "Permission denied, please try again." It's possible to prevent this from happening by whitelisting your own IP addresses. See http://forums.cpanel.net/f5/cant-login-whm-ssh-216472.html for more details.
If it's still possible to login via SSH but not via WHM anymore, please take a look at this article: http://docs.cpanel.net/twiki/bin/view/11_30/WHMDocs/CPHulk