If your site gives an error or the pages of the site do not open, you need to establish the cause of the problem.
The first step is to check the - error_log - the site's error log.
cPanel creates an error log in the root directory of the site.
Login to cPanel - File Manager.
Open the site directory.
In the site directory you need to find the file - error_log.
Click on it with the right button and select - View.
In the error log, you can see the reason for the 500 error on the site.
PHP Parse error: syntax error, unexpected 'define' (T_STRING) in /home/exampleaccount/public_html/index.php on line 14
The reason for the error is clear. Editing of the index.php file was made with errors. It is necessary to correct the errors in the file and check the operation of the site.
In this way, you can independently restore the site.