Recently I’ve been experiencing a Magento admin login problem in Chrome. The problem is that when I enter the correct username and password on the Magento admin login screen it simply returns back to the same screen. This was when working locally using http://magento/my-site as the domain name.
Simple. The problem occurs because the domain name isn’t a fully qualified domain name and so the browser won’t accept the cookies. Simply change the domain name to one with a dot in it (a period for the American readers). Once I’d changed it to http://magento.local/my-site it worked perfectly.
Based in Staffordshire, UK