I just found If I use the same email to create different account Magento would just reload the same page
www.domainName.com/index.php/customer/account/create/. And there is no new account being created in the backend.
I found there should be something like a warning message saying
"There is already an account with this email address. If you are sure that it is your email address, <a href="%s">click here</a> to get your password and access your account.'"
how do I fix this problem. thank you.