Try that:
# Listen for virtual host requests on all IP addresses
NameVirtualHost *:80
<VirtualHost *:80>
DocumentRoot "C:\xampp\htdocs"
ServerName _default_
</VirtualHost>
<VirtualHost *:80>
DocumentRoot "C:\xampp\htdocs\newdomain"
ServerName www.newdomain.com
</VirtualHost>
You need a default virtualhost, that's the catch_all thing, when the Host Header defined in the HTTP query does not match any ServerName
directive the default VH is useD. And the default VH is the first one defined in the configuration.