Additionally, check your network requests page (on Chrome and many other browsers just click F12, then go to “Network” and reload the page) to see if you see a 500 error. If so, enable PHP errors using this:
That should help you debug if you are indeed getting an error (by default PHP error info is disabled to prevent leaking information).
Your page is still replying with a status code 500, meaning your PHP code contains bug and crashed. You might be able to get the homepage working, but 500 can occur anywhere else on your website. Please check you code for all pages using the same advise above.
If you need help with your code, share it with us and we’ll look into it for you. Remember to remove credentials and format your code before your post.