Restart machine:

/sbin/reboot

Restart Apache

/etc/init.d/apache2/restart

Check IP addresses:

ifconfig

This was all trying to add two new IP addresses to Apache, on a Ubuntu box over Putty. I found that I needed to edit /etc/apache2/ports.conf and add
Listen <IP>:80 for the new IP addresses.

About 2 days downtime trying to figure it out, but got it eventually.