Internal Server Error, famously called HTTP 500 Error, will appear for many reasons – even that are beyond WordPress. This is not particular to WordPress and as such is a generic error. However, it is important to make sure if this comes because of WordPress – for instance installing a new plugin or a new theme or editing .htaccess file could end up with this error.
Solution
Resolving coding error in .htacess can help in resolving the error. If you do not know how to resolve the code error, you can simply change the filename of .htaccess file and then load your website. Chances are that it might load correctly – in that case it is for sure that .htacess has coding errors that needs to be resolved.
Internal Server Error is also caused because of incorrect permission on one or more files or folders. Make sure the permissions confirm to the WordPress standards. For example, all directories should have 755 or 750 permission and all files should have 644 or 640 with an exception to wp-config.php file which should have 400 or 440 permission.