Error in public_html/wp-blog-header.php on line 14

Dear WordPress Forum,
Please can somebody help me sort out this problem.
The site was working well, no changes made me, as I’m not a programmer.
THe site is called:
https://www.international-club-andorra.com
All I can see now is,
Fatal error: Call to undefined function wp() in /home/interna/public_html/wp-blog-header.php on line 14

I’ve asked my WHB – WebHostingBuzz to use a back up of the site asap.

That doesn’t solve the problem, but at least we’ll be on-line again.
Thank you in advance Jan