Can't log in to Magento Admin

I managed to fix it! I found this solution here: http://blog.chapagain.com.np/magento-admin-login-problem/.

I wanted to know why that fixed it though and var_dumped the items I commented out and realized that the cookie domain was being set to just '/' and we have magento set up under '/shop/'. So I went to the configuration section (having managed to log in after commenting out the 3 lines mentioned in the article), changed the Cookie Domain and Cookie Path to be blank and saved. I then uncommented those lines and tried again and all's working well!

In new Magento Installation, do the following ->

Open the file

app/code/core/Mage/Core/Model/Session/Abstract/Varien.php.

and change the code at line 87 to this ->

    $cookieParams = array(
        'lifetime' => $cookie->getLifetime(),
        'path'     => $cookie->getPath(),
      //  'domain'   => $cookie->getConfigDomain(),
      //  'secure'   => $cookie->isSecure(),
      //  'httponly' => $cookie->getHttponly()
    );

I have also encountered this issue. This is what I did : In core_config_data, delete any rows where path = web/cookie/cookie_domain