Windows 2008 firewall
Windows Server 2008 by default does NOT reply to ping packets (which
technically are ICMP packets).
To enable this to go:
Administrative Tools - Windows Firewall with Advanced Security
Scroll down to File And Print Sharing (Echo Request - ICMPv4-IN) (or v6 if you are using ipv6)
Enabled this rule
Generally ICMP and Ping is useful for quickly checkig if machines are up/down, i.e. during a reboot pinging it. Leaving it off secures you by reducing the attack surface which I'm sure is why it's off by default.