There are a number of reasons your website at your domain may not be working.
1) If you are seeing a 'Server not found' error in your browser and/or are also having issues with other services at the domain like email there may be a DNS issue. Please check our FAQ entry Why is my domain not working? and check all possible causes there.
2) If you have cPanel hosting with us check to see if you can access your cPanel at all - you might simply be unable to connect from your location due to a block of your local IP; is my local IP blocked?
3) If you are getting any of the following HTTP errors in your browser refer the issue to your web master. If you have cPanel hosting with us you have access to the 'Error Log' tool for further details:
500 - Internal Server Error: This indicates your website is asking the server to do something it can't. If you have a .htaccess file this is a good place to start with checking for any errors.
404 - Not Found: This indicates a broken link somewhere in your site; your website is trying to load a file/page that is simply not there.
403 - Forbidden: This error is related to permissions; the resource you have asked for doesn't have the correct permissions set for you to be able to view/retrieve it.
4) If you are getting any PHP errors like 'memory limit exceeded' you can change PHP settings via the appropriate directives in a 'php.ini' file or in the appropriate configuration file for your website (e.g. if using Wordpress and you need to increase your PHP memory limit). See our How do I change PHP settings? FAQ entry for more details.