Magento 1.9: Login / Registration form not working

I know that you already inserted the formkey, but I had the same problem and I discovered that I was using the formkey in the wrong way.

1 - Make sure that you use this code to insert the formkey:

<?php echo $this->getBlockHtml('formkey'); ?>

2 - The code should be right after the line:

<form action="<?php echo $this->getPostActionUrl() ?>" method="post" id="login-form">

3 - Make the change in the right files:

app/design/frontend/base/default/template/customer/form/login.phtml
app/design/frontend/base/default/template/customer/form/register.phtml

or, if you are using a custom theme:

app/design/frontend/COMPANY/THEME/template/customer/form/login.phtml
app/design/frontend/COMPANY/THEME/template/customer/form/register.phtml

Good luck :)