If you are connected to the Internet but are unable to connect to Yahoo Messenger 11.5, your Messenger or Internet Explorer settings may be the problem. Yahoo Messenger uses the Internet Options settings of Internet Explorer to connect to the Yahoo servers. Furthermore, the security settings in Internet Explorer may cause problems when Yahoo Messenger attempts to communicate with its servers. If all settings are correct and you still can't log in to Yahoo Messenger, you may need to reinstall the software. Note that the Connection Troubleshooter that displays when Yahoo Messenger encounters connection problems can help you fix some of the problems.
Yahoo Messenger Connection Settings
Launch Yahoo Messenger, click "Messenger" and choose "Connection Preferences" to launch the Yahoo Messenger Preferences window.
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Click "Connect directly to the Internet" if you are not using a proxy server. If you are using a proxy server, click "Connect via a proxy server" and then click "HTTP proxy" or "SOCKS proxy" to select the type of proxy server. Type the correct server name, port number, user ID and password into the relevant fields.
Change the Internet connection type from the "Internet connection" drop-down box. You can choose "Dial-Up," "Broadband (DSL/Cable)" or "High-speed (T1/LAN)."
Click "OK" and then log in using the correct Yahoo username and password combination.
Internet Explorer Connection Settings
Launch Internet Explorer and navigate to the Yahoo homepage (link in Resources). If Internet Explorer can't display the page, verify its connection settings.
Click the gear icon and choose "Internet Options" from the menu to display the Internet Options window.
Click the "Connections" tab to view the network connections used by Internet Explorer to connect to the Internet.
Select the active network connection and click the "Settings" button. Ensure the settings are correct. If you are using a proxy, check the "Use a proxy server for this connection" and then enter the proxy settings into the "Address" and "Port" fields. Click "Advanced" to change the advanced settings of the proxy server.
Click "OK" to close the Connections Settings window and then click "OK" to close the Internet Explorer window. Log in to Yahoo Messenger using your Yahoo username and password.
Yahoo Messenger Login Server Issues
Launch Internet Explorer, click the gear icon and choose "Internet Options" from the menu. Click the "LAN settings" button to open the Local Area Network Settings dialog box.
Check "Use a proxy server for your LAN" and then input the address and port into the "Address" and "Port" fields.
Click the "Advanced" button to configure the advanced settings of the proxy. Enter the proxy settings into the appropriate fields and ensure the Secure and Port settings are correct.
Click "OK" three times to apply the new settings and close all windows. Log in to Yahoo Messenger.