Going down on a site with "Firefox can't establish a connection to the server"

I've a site that constantly goes down with the message below.

Unable to connect

Firefox can't establish a connection to the server at

• The site could be temporarily unavailable or too busy. Try again in a few moments.
• If you are unable t开发者_如何学JAVAo load any pages, check your computer's network connection.
• If your computer or network is protected by a firewall or proxy, make sure that Firefox is permitted to access the Web.

What are the possible reasons that's causing this message to be shown?

The hosting is saying the script is taking too much memory. Is this really the case?

To start troubleshooting replace your index.php (being sure to keep a copy of the original) with something as basic as <?php phpinfo(); ?> and see if that works consistently.

If it does (assuming it is something in your index.php) you can start working through your original index.php adding a bare-bones framework to start with and add more code until eventually it breaks.

Troubleshooting is easy if you start from one end or the other and work towards the "trouble". In this case, start with minimal code, keep adding until something goes wrong.