It could be sysctl or your firewall. Have a look in /etc/sysctl.conf for a line like this:
Code:
net.ipv4.icmp_echo_ignore_all = 1
You can set this to 0 instead of 1 and reload the change with
sysctl -p. If that doesn't work, have you checked your iptables settings to see if the pings are being dropped by your firewall? Often, iptables logs to one of the /var/log/{syslog,messages} files - there may be info in there.