By default windows server 2008's firewall blocks ping requests.
Here is how you can enabled it:
1) Open the windows firewall console.
2) Click inbound rules.
3) Find "File and Printer Sharing (Echo Request - ICMPv4-In)" and click enable rule. (if you need IPv6 you will need to enable that too)
Or by command line:
netsh firewall set icmpsetting 8