WordPress blog or website might start to show 500 Internal server error if for example there will be incorrect file permissions or due to bad entries in .htaccess file.

In order to troubleshoot this issue, browse WordPress files with any file manager provided by hosting provider of FTP client like FileZilla. Generally, permissions for files should be 644 and 755 for the folders. We can check which exactly file or folder has wrong permission by checking Apache error log.

Another reason why website is showing 500 internal server error might be caused due to wrong directive in the .htaccess file. This file is located in WordPress installation directory. Simply open it for editing and check for bad directives that might be conflicting with web server. The easiest way to fix it, is to comment out line by line and check how website is working. This way it's possible to locate the line that causes 500 error.