Fatal error

Hello

I’ve just updated to WordPress 3.7 and I’m getting a fatal error message. I can’t access my dashboard or about pages, or even log in. All it says is: “Fatal error: Call to undefined function wp_initial_constants() in /home/kassiast/public_html/wp-settings.php on line 26”.

I didn’t set up the site myself and I’m not very technologically minded but would love to get the site back up and running. Is there anyone who can give me any help?

Many thanks in advance!

Kassia