Your problem may be that you don't have a browser feature called 'cookies' turned on. Cookies are required to use Weatherzone and can be activated in your browser's secury preferences.
In internet explorer, make sure both your security and privacy settings are set no higher than 'medium'. These preferences can be changed in 'internet options' in the 'tools' menu.
Lastly, make sure that you have ticked the 'remember me' box when you log in