Note that if "cookies" are disabled on your browser, the signin will not work either. It is somewhat uncommon for this function to be disabled without the user choosing so, but it is worth checking. The location of this setting varies, but in Internet Explorer for Windows, it is usually found at Tool Menu > Internet Options > Privacy Tab. In this case, the "Medium" setting is sufficient. No personal information is involved in this function, and the cookie file disappears when the browser is closed.
