Starting apache fails (could not bind to address 0.0.0.0:80)

Worked for me running this command:

fuser -k -n tcp 80

It may be skype or nginx using the port 80.

Try shutting down skype, or running: sudo /etc/init.d/nginx stop

I had the same error, and just want to confirm that running

    sudo netstat -ltnp | grep ':80'

helped me indicate that Hiawatha webserver was in the way of Apache2.

Removing Hiawatha fixed the issue (sudo dpkg --purge hiawatha). Ubuntu 12.04.2 server.