You are correct oogee, updating a website is pretty simple, for anyone only if you have CMS on your site and one knows how to use it.

So, to me looks like someone was/is playing with the files on server and was incorporating some changes to the site or maybe even updates (updates? that would be sweet). IMO of course.

The "500 Internal Server Error" can be coused by:

1) The file has wrong permission:

- The filemust have permissions CHMOD644

- For safety reasons all PHP files must have exactly such powers

- Files uploaded via FTP automatically receive the appropriate rights

2) The directory in which the file is, has the wrong permissions:

- Directory should have chmod 755

- For safety reasons, all directories must have exactly such powers

- Catalogs established from the FTP or hosting control panel automatically have the appropriate rights

3) File name .htaccess contains variables:

- php_admin_value

- php_value

- php_flag

Such variables are not interpreted by the server and must be removed. If you need to change the value of the variable for PHP contact to do this with us, and set the appropriate values ​​for your account

4) The file .htaccess is a directive Options All or has it turned on ExecCGI variable.

Wrong settings:

All Options

Options ExecCGI

Examples of the correct settings:

Options Indexes Includes MultiViews

ALSO

Error with an .htaccess file

If you are using a .htaccess on your site, it may be interfering with the web page you are trying to load into your browser. Please double check the .htaccess configuration. Any syntax errors will cause a 500 Internal Server Error message to be displayed instead of your website.

To confirm whether a misconfiguration .htaccess is the cause of the 500 Internal Server error, either remove or rename the .htaccess file temporarily and then try to reload the page.

AND

http://www.prestashop.com/blog/en/the-500-internal-server-error-explained-solved/

cheers