How to Troubleshoot Your Firewall and Proxy Settings When Using Skype
Run your Skype incoming connections through ports 80 and 443: If you are having difficulty connecting to the Internet over Skype after establishing your proxy settings, look to see that a check mark appears next to Use Port 80 and 443 as Alternatives for Incoming Connections.
You can find this setting by choosing Tools→Options→Advanced and clicking Connection from the list of options in the left panel. If the Use Port 80 and 443 as Alternatives for Incoming Connections option is not checked, select it, save your settings, and retry Skype.
Open your external firewall: If your company is running an external firewall, ask your network or security administrator to configure the firewall to allow for Skype traffic.
Open your internal firewall: If you are running your own personal firewall and have administrative rights on your computer, here are some steps you can take:
Check to see whether there is currently a rule that specifically prohibits Skype traffic. The first time you ran Skype, your personal firewall server may have prompted you when it detected Skype traffic and suggested that it be blocked. If you gave the OK to block the traffic, Skype cannot communicate with the outside world. Your solution is to find the offending rule and remove it.
If you can't find the rule that blocks Skype, the following may work: Uninstall Skype and re-install it. The next time Skype runs, your personal firewall may prompt you about what to do. This time, you can tell it to allow the Skype traffic.
Your personal firewall software may not have any rules about Skype and may need to be explicitly told that network traffic associated with Skype should be allowed. You must add Skype to your firewall's list of allowed programs.
Some companies require you to apply special settings to connect your Web browser to the Internet. Generally, your Skype Connection settings should closely match those of your browser.