unable to create new mail in thunderbird & play video on youtube

dear friends,
i can't create a new mail set up in thunderbird, it gives me an error massage"sorry-we are unable to communicate with our sign up server-please check your connection." and my second problem is that i can't play video on youtube, it also gives an error massage. my network connection is ok. i can surf net without any problem. please help me to solve my prob. thanks a lot.