My firefox is the latest updated version i.e. 3.6.17, but it can't open the yahoo sign in page and not even the sign up page is opening.

I have tried by deleting all cookies, cache and also try to disabling all plugins and add ons ... I have tried running the ff in safe mode... but only the yahoo sign in or sign up page is not loading.. even I have tried by uninstalling the whole Firefox and again reinstalling the latest version ......... but nothing can solve the problem ... plz provide a solution...