ICMP echo requests, used for ping command are blocked in Windows 7 firewall by default. If your talking of a pc connected directly to the internet then the pc's IP address will be the external address assigned by your ISP and it will be dependent solely on your firewall for defense. If you are connected via a router then the NAT in your router which translates messages from the external address to your private internal address protects you as internal addresses cannot be seen outside of the router. You may find though that the router itself responds to ping requests, depending on the make and model and how you have configured it.
If you want to assess your machine state try running a full set of tests on your pc at shields up: