It is enabled by default, however I can't tell it's not enabled, because
If you google for "enable icmp in windows", all you get is how to open a port on the firewall, but that assumes that your icmp daemon/service is enabled, but how do you enable it?
The process that listens to port 7 to ICMP echo requests is called TCPSVCS.EXE
You can try calling "C:\Windows\System32\TCPSVCS.EXE" to see if it works and starts listening to ICMP echo requests.
The service that start this process is called simptcp, just enable it.