"I am registered user but I cannot sign in".
You need to clear cache in your internet browser.
Mozilla Firefox
Options > Privacy > Clear your recent history or press CTRL+SHIFT+DEL and choose clear cache.
Google Chrome
Settings > Privacy > Clear browsing data or press CTRL+SHIFT+DEL and choose clear cache.
Internet Explorer
Settings > Safety > Delete browsing history or press CTRL+SHIFT+DEL and choose clear cache.
