Date won't load with 500 server error on all pages and queries

I am have trouble with data queries, all my pages are retuning this error:
Failed to load resource: the server responded with a status of 500 (Internal Server Error)

here is a link to a sample page:
http://backend.zaprompt.com/untitled.php

What could be causing this. When I test the database connections it is successful and as far as I know nothing on my server was changed.