[Ubuntu]: Can't open any port

I followed the following guide:

https://www.digitalocean.com/community/tutorials/how-to-set-up-a-firewall-using-ip-tables-on-ubuntu-12-04

and tried to open port 80, but I still have nothing open or listening:

netstat -plunt
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 127.0.0.1:3306          0.0.0.0:*               LISTEN      1051/mysqld     
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      965/sshd        
tcp6       0      0 :::22   

The strangest thing is that I could connect to the server yesterday and today it isn’t working anymore and the only thing I changed was to add a DNS entry on Digital Ocean.

Could this have anything to do with it?

I tried even to disable any protection with the following commands:

$ sudo iptables -X
$ sudo iptables -t nat -F
$ sudo iptables -t nat -X
$ sudo iptables -t mangle -F
$ sudo iptables -t mangle -X
$ sudo iptables -P INPUT ACCEPT
$ sudo iptables -P FORWARD ACCEPT
$ sudo iptables -P OUTPUT ACCEPT

but still only port 22 is accessible. What could be the reason for this?