There are a few possible causes of the 500 Internal Server Error. It is not always due to WordPress, however this article addresses the WordPress culprits. This knowledgebase article addresses non-WordPress related causes of 500 Errors.
Create A New .htaccess file
- In cPanel, find the Files section. Click "File Manager".
- Put a checkmark next to "Document Root", and choose the domain name that you wish to work with.
- Check "Show Hidden Files (dotfiles)".
- Click "Go".
- Find your .htaccess file in the list. Right click on it.
- Select "Rename", and rename the file ".htaccess.bak"
- Log in to your WordPress administration account.
- Click "Settings" on the left hand side, and then select "Permalinks".
- Check to make sure the settings are correct.
- Click "Save Settings".
- Reload the side to see if the 500 Error persists.
Deactivate and Reactivate All Plugins
- In cPanel, click on the File Manager icon.
- Select "Web Root (public_html/www)", "Document Root" for the domain you have WordPress installed to, and select "Go".
- Expand the "public_html" folder, and find the "/wp-conent/plugins" folder.
- Right click on "/wp-content/plugins", and rename it "plugins.old".
- Now right click on "/wp-content/plugins.old" and rename it "plugins"
- Log in to your WordPress administrative panel, and reactivate each plugin one at a time, refreshing the website to see if the 500 Error comes back. If it does, you have identified the plugin at fault.