Recent Windows Updates and other program changes can cause the default Windows Firewall to activate.  This is a problem if running another Firewall program since trusted Programs can be blocked and stop working properly when trying to access the Internet.  It is recommended to use a 3rd Party Firewall which has been tested to successfully defeat firewall termination  attacks.   To verify if the Windows Firewall is active see the detailed instructions found at page III-66 of the Computer Appliance Learning Maintenance Manual OR the quick guide for XP is to LEFT-CLICK on START, LEFT-CLICK on Control Panel, LEFT-CLICK on Windows Firewall.  In Vista, LEFT-CLICK the PEARL, type Security Center and press ENTER to reach the Windows Firewall settings.   If it is Green and active AND you ARE using a 3rd party Firewall go ahead and LEFT-CLICK on Off and LEFT-CLICK on OKAY.