1)Make sure you have latest version of Skype. It can be found here: http://www.skype.com/download/
2) Close Skype
3) If you have router, please reboot your router
4) If you are behind proxy server, make sure you have set all proxy settings in Internet Explorer --> Tools --> Internet Options --> Connections --> LAN settings and in Skype under Tools --> Options --> Connection
5) If you are using windows built-in firewall,
Go to Start menu --> Settings --> Control Panel --> Windows firewall
If 'Don't allow exceptions' is ticked, please untick it.
Go to the 'Exceptions' tab
If there is Skype listed below, delete it.
Start Skype, you will be prompted to allow Skype to connect to internet, accept it.
6) If you are using some other firewall,
Go to Start menu --> Programs and select your firewall
Make sure that exceptions are allowed.
Go to 'Exceptions' tab
If there is Skype listed below, delete it
Start Skype, you will be prompted to allow Skype to connect to the internet, select 'Yes'
7) Start Skype
If it does not help, please have a look at our troubleshooter which addresses this error:http://support.skype.com/?_a=troubleshooter