All virtualhosts serving Apache default files

In virtual host definition file, correct the line below.

ServerRoot /home/empression/Projects/billmed/web/httpdocs to DocumentRoot /home/empression/Projects/billmed/web/httpdocs

Use DocumentRoot directive to serve virtualhost. here is the link for more information http://httpd.apache.org/docs/2.2/mod/core.html

Update your virtualhost definition (/etc/apache2/sites-enabled/billmed) as following,

<VirtualHost *:80>
 ServerName billmed.emp
 DocumentRoot /home/empression/Projects/billmed/web/httpdocs

 <Directory "/home/empression/Projects/billmed/web/httpdocs">
  Order Allow,Deny
  Allow from All
 </Directory>
</VirtualHost>

@yasin is correct; you need to have your VirtualHosts specify a DocumentRoot ('...the directory from which httpd will serve files...')not a ServerRoot ('...the directory in which the server lives. Typically it will contain the subdirectories conf/ and logs/....')

There might be another problem also, but that part is definitely wrong.