redirect web server with no-ip and port forwarding in livebox

I want my Apache web server running on a Livebox (home router appliance running Linux) to be accessible from the Internet (WAN). I installed and configured the application noip2 on my Ubuntu PC. When I ping my hostname, it redirects me to my WAN ip, which is what I wanted. But I cannot access my Apache web server. I tried this: - Disabling the iptables firewall configuration or the firewall of my Sagem modem. - Port forwarding on sagem modem (NAT). - Configuration of Apache. What else can I try? How can I make my web server accessible from the WAN side?