In my case, I had thoughtlessly installed the 'nginx' server on my Ubuntu system -- which then grabbed the 127.0.0.1:80 port from apache2.
When I changed /etc/apache2/ports.conf values of
and got apache2 started, both servers were then up: nginx at 127.0.0.1:80 and apache2 at 127.0.0.1:8080
So I simply uninstalled nginx (also nginx-full and nginx-common) -- and set /etc/apache2/ports.conf port values back to default. Apache is now at 127.0.0.1:80. Knock on wood.