If you are experiencing any issue on your Yahoo mail account such as your Yahoo mail is not working properly, then you need to check your Yahoo mail server status. Is Yahoo mail down or not. If everything is ok, you need to restart your devices and also check your internet connection, because sometimes due to all these reasons Yahoo mail goes down.

See also - http://www.onlinegeeks.viamagus.com/blog/Is-Yahoo-s-Website-Down-Right-Now.html