Site offline daily and have to reinstall 4.4 every time

Internal server errors (error 500) are often caused by plugin or theme function conflicts, so if you have access to your admin panel, try deactivating all plugins. If you don’t have access to your admin panel, try manually resetting your plugins (no Dashboard access required). If that resolves the issue, reactivate each one individually until you find the cause.

If that does not resolve the issue, try switching to the Twenty Fifteen theme to rule-out a theme-specific issue. If you don’t have access to your admin panel, access your server via FTP or SFTP, navigate to /wp-content/themes/ and rename the directory of your currently active theme. This will force the default theme to activate and hopefully rule-out a theme-specific issue.

If that does not resolve the issue, it’s possible that a .htaccess rule could be the source of the problem. To check for this, access your server via FTP or SFTP and rename the .htaccess file. If you can’t find a .htaccess file, make sure that you have set your FTP or SFTP client to view invisible files.

If you weren’t able to resolve the issue by either resetting your plugins and theme or renaming your .htaccess file, we may be able to help, but we’ll need a more detailed error message. Internal server errors are usually described in more detail in the server error log. If you have access to your server error log, generate the error again, note the date and time, then immediately check your server error log for any errors that occurred during that time period. If you don’t have access to your server error log, ask your hosting provider to look for you.

None of the above solutions worked. My server error log reads as follows:

[Mon Dec 21 04:43:43 2015] [error] [client 62.149.144.15:52959] – https://www.psmtickling.com – End of script output before headers: index.php
[Mon Dec 21 04:43:43 2015] [error] [client 62.149.144.15:52959] – https://www.psmtickling.com – AH01215: suexec policy violation: see suexec log for more details: /web/htdocs/www.psmtickling.com/home/index.php

I use FileZilla, but I have no idea where “/web/htdocs/www.psmtickling.com/home/index.php” is.
The software doesn’t either display the directory or find it with its search engine.

I suspect that’s WordPress’s main index.php file.

If FileZilla is configured to go directly into the account, it may not display the full server path.

Try downloading WordPress again and delete then replace your copies of everything except the wp-config.php file and the /wp-content/ directory with fresh copies from the download. This will effectively replace all of your core files without damaging your content and settings. Some uploaders tend to be unreliable when overwriting files, so don’t forget to delete the original files before replacing them.

James, thank you so much for your patience and time.
I looked at the very first “index.php” file inside the newly downloaded WordPress 4.4 folder and it was as simple as this:

<?php
/**
 * Front to the WordPress application. This file doesn't do anything, but loads
 * wp-blog-header.php which does and tells WordPress to load the theme.
 *
 * @package WordPress
 */

/**
 * Tells WordPress to load the WordPress theme and output it.
 *
 * @var bool
 */
define('WP_USE_THEMES', true);

/** Loads the WordPress Environment and Template */
require( dirname( __FILE__ ) . '/wp-blog-header.php' );

While the same kind of file I had uploaded on FileZilla was the following:

[removed]

Even for an amateur like myself, this one looks radically different and pretty weird, compared to the original one that is supposed to be there, and all that code gobbledygook seems quite suspicious.
Could this be the problem?
Well, at least, what’s apparent is I’ve changed this to the official code of the index.php file and, for now, it seems to have brought my site back.

Ok, that code at the top is a hack attempt.

Remain calm and carefully follow this guide. When you’re done, you may want to implement some (if not all) of the recommended security measures.

For the moment, I haven’t had any problem again, so I’ll set this as resolved. Thank you!

You’re welcome!