If I were paying for a managed server and they told me
This indicated that the Apache service on your server is no longer running. You can restart this via SSH using the command "service httpd restart". I would recommend reviewing your servers logs in /var/log/ as they will indicate the issues/errors that this service is experiencing causing it to crash.
I'd tell them bye.

You can see the error logs from the cpanel in the section labeled Logs.

All that said, there's nothing about Zen Cart that should cause this to happen. You might want to search the forum for your hosting company's name and see if there are other horror stories out there.