fatal error for header

Here’s my site http://romancebox.org/index.php, and I keep getting this error message:

Fatal error: Call to undefined function: get_header() in /home/brenda/public_html/index.php on line 1

I can’t even log into my account because it also shows that message. In line 1 of my index.php, here’s what I have:

<?php get_header(); ?>

What is wrong?