Excuse me, but "No signal" is a cellular message you get when you are to far away, or shielded from, the cellular relays.
If you try to access Yahoo.messenger from your cellular or smart phone, please repost in the Telephone: Mobile Phone section.
If you use a computer and use wi-fi to connect, check that you get an effective connection and can access other web pages.
If you use a computer and have good wi-fi or use whired connection, I would suspect that somebody planted some prank programm on it as a joke on you.
Electro, July 2011
