You might want to answer the following questions:
- What makes you think port 80 is "blocked"?
- Is it possible that some other app 'owns' port 80? (Some other app compared to what?)
- Then there is the issue of firewall rules. Do your existing rules look as if they should allow port 80 access?
What is your Distro? Specifically is it something that uses App Armor or SELinux?