I always forget where to change the ping setting in the Windows Server 2008 R2 Firewall.
To enable ping

Go to Start >> Administrative Tools >> Windows Firewall with Advanced Security >> Inbound Rules >> File and Printer Sharing (Echo Request – ICMPv4-IN) >> right click and select Enable Rule.

To disable the ping rule just select Disable Rule in the last step.
These steps does also work in Windows 7 to enable ping.