Error 500 is perhaps the most common of all errors on the web. It is not WordPress-specific and not very informative. You could try the following to resolve it.
Re-upload the WordPress Core Files.
Deactivate all Plugins - especially the most recently uploaded ones.
Check for Corrupt .htaccess File and if it contains any illegal commands.
Switch your WordPress site to the default theme.
To gain more insight into the errors you could have a look at the cPanel error log under 'Errors'.
Also, try debugging your website by setting the debug to true in your wp-config file.