If you are using Server Side Includes SSI in your files and it's not working, you most likely need to enable them in your .htaccess file.
Steps to enable SSI:
Find your .htaccess in your public_html and edit it with the code editor of your choice. Paste the following code in the .htaccess towards the top of the page:
AddType text/html .shtml
AddHandler server-parsed .shtml
Options Indexes FollowSymLinks Includes
AddHandler server-parsed .html .htm
Visit your website. You should see the SSI Server Side Includes working now.