WARNING:
Resetting the Windows Firewall is easy, but will often cause many more problems, then it resolves.
The "Restore defaults" link available in the left column will automatically reset the firewall settings, but then you will have to go into "'Advanced settings" and redefine many of your inbound and outbound rules to support many of your third party programs, like Skype, Itunes, etc. as well as some of the rules with regard to your core networking components like file sharing, ICMP echo, etc.
If you suspect that the Windows firewall is causing a specific issue with your computer, then perhaps we would be better off addressing that specifically