I recently had a Windows computer, using Chrome get stuck where I could not log into my local magento installation. I then tried to log into the admin, and it appears as though things worked fine, but the login page reloads, with no error or messaging. Welcome to COOKIE purgatory.
Turns out that Chrome, being somewhat neurotic, does not like something about the configuration and/or the domain that the cookie is set.
Step 1: Using some sort of method to update the mysql database ( adminer, phpmyadmin, command line )
Update core_config_data 2 paths and set the values to null
UPDATE `core_config_data` SET
`value` = NULL
WHERE (`config_id` = '37' COLLATE utf8_bin) OR (`config_id` = '44' COLLATE utf8_bin);
Problem fixed! I can now log in as a customer on the frontend and log into the admin section of Magento!