A sua pergunta parece ter sido completamente respondida aqui :
Internet Explorer is used to sign into Yahoo Messenger. If you have another browser set as default, IE will still sit as a link between your browser and Yahoo Messenger. For this reason most troubleshooting is concentrated on Internet Explorer.
Upgrade IE and update any support software (Flashplayer, Java, Shockwaveplayer)
On the sign in page, click 'Messenger' > Connection Preference. Toggle between 'Connect direct to the internet' and 'Proxy setting' to make sure the information is correct in the lower 2 boxes.
Check these settings in IE (even if you have another browser set as default):
- Tools > Internet options > Connections > Lan settings > check 'Automatically detect settings - uncheck other options.
- Tools > work offline - make sure this is NOT checked and has a red X through it
Disable your firewall and test to see if you can sign in.
Control Panel > Internet Options > Connections > LAN Settings > Uncheck Proxy server, check automatically detect settings.
Control Panel > Internet Options > Connections > dial-up and virtual private Network setting > select your default connection > setting > check automatically detect setting
If you are unable to sign into this secure page: https://login.yahoo.com/config/login?.src=fptx._intl=uk. Copy the yahoo https address above and paste it in:
IE > tools > internet options > LAN settings - check automatically detect settings > Advanced - paste in 'Secure' window > OK