website without www is 404

[apinto]

It can have multiple causes, are you using any particular software on your website (like wordpress, joomla, etc)? Sometimes they change the .htaccess and might cause issues.

Quick Fix for .htaccess:
Try adding this to the .httaccess file (however this is probably NOT what you should fix, read below):

Code:

RewriteEngine on
RewriteCond %{HTTP_HOST} !^www\.
RewriteRule ^(.*)$ http://www.%{HTTP_HOST}/$1 [R=301,L]

Probably your issue is related to the DNS  or VHOSTS  setup, please check the following:
DNS Setup:

1. You have a A Record entry for yourdomain.com and for www.yourdomain.com.
   
2. Both entries are using the same IP Address (either IPv4 and/or IPv6 if applicable).
   

NOTE: Your DNS setup might be using Sentora Bind9, CloudFlare, Your Registar or your Hosting Provider, it only needs to be changed on ONE of those places, it's up to you do know witch one you are using.

V-HOSTS Setup:
You should have something like this on your V-HOSTS file for yourdomain.com

Code:

<VirtualHost *>
 ServerName www.yourdomain.com
 ServerAlias yourdomain.com
</VirtualHost>

What you need to check is the ServerAlias directive, the rest is here only for reference.
Please note that your VirtualHost may differ a LOT from the above example (usually it has much more lines).

Hope this helps you.