If you’re running Windows XP, you might be running XP's built-in Windows Firewall without your knowledge, since it’s the default. Sometimes this blocks your webcam. Follow these steps to ensure that the correct ports are opened.

1. Click "Start," "Settings," and select "Control Panel."
2. Double-click the "Network Connections" icon.
3. Right-click the connection that you use to connect to the Internet, and then click "Properties."
4. On the "Advanced" tab, uncheck the "Protect my computer" checkbox if you want to disable the firewall. If you would like to open connectivity to for just this specific port, ensure the box in front of your adapter is checked and continue below:
1. Click the Advanced tab.
2. Under “Network Connection Settings”, click the settings button.
3. Select the Services tab and click Add.
• Description of Service:
  Yahoo! Webcam
• Name or IP address of the computer hosting this service on your network:
  127.0.0.1
• External Port number for this service:
  5100
• Internal Port number for this service:
  5100
• Ensure TCP is selected.
4. OK! Click OK (3 times) to return to control panel.