Sounds like a network problem. Are you using a proxy server or firewall? Are you in a work setting, or at home? Many businesses block the ports typically used for audio/video as a matter of routine, so if you're attempting this from work, you should check with your IT group to make sure it's permitted.
If you're trying from home, you might be experiencing a problem with a firewall or proxy. Try temporarily disabling to test.
Where are you located? Some countries also block audio/video calls, sometimes to prevent citizens from using free alternatives to government-run telecom.