Try to find

#ServerName www.example.com:80
and change to

ServerName "YourServerName"
and...

PHP Code: 
<VirtualHost *:80>     # Admin email, Server Name (domain name) and any aliases   ServerAdmin webmaster@domain1.com   ServerName  domain1.com   ServerAlias www.domain1.com       # Index file and Document Root (where the public files are located)   DirectoryIndex index.html   DocumentRoot /home/demo/public_html/domain1.com/public       # Custom log file locations   LogLevel warn   ErrorLog  /home/demo/public_html/domain1.com/log/error.log   CustomLog /home/demo/public_html/domain1.com/log/access.log combined   </VirtualHost>