I've got a VPS along with a domain title registered using the provider.
After I enter world wide web.example.com my website is displayed properly, but entering example.com doesn't work. I can ping world wide web.example.com.
I added the next line to my apache2 default vhosts file:
ServerName example.com ServerAlias world wide web.example.com
But this didn't work.
The VPS is really a Debian5 OS.
Note: There's no option using a provided user interface to include this, it is a fundamental package I bought
Look at your DNS first (search/nslookup)
search world wide web.example.com search example.com
Odds are example.com is not mentioning to anything, or perhaps a different host, CNAME or ip.
Give a catch all record if you want: *.example.com
How you can manage DNS is dependent in your Web service provider/Host company