Installed at public_html/drupal, but website only opens with

I have installed Drupal at public_html/drupal, but when I go to, I get the following error:

The website cannot display the page

 HTTP 500

Most likely causes:

  • The website is under maintenance.
  • The website has a programming error.

However, if I go to, I get to the drupal login page.

What have I done incorrectly? Thanks in advance.

Drupal version: