Fatal Error! Help!

My db server has had known problems today but I think it may be fixed as another wordpress website I recently set up on the same server seems to be running ok. However my own website is returning the following error when trying to hit the home page:

Fatal error: Call to undefined function get_header() in E:\domains\f\followtheboat.com\user\htdocs\index.php on line 1

Line 1, of course, is the call to the head page:

<?php get_header(); ?>

Neither the index or header files had any code changed.

If there is still an issue with the database server (I’ve not received a response from my host) then could this be a possible error or has something got corrupted when the server went down that now needs fixing now the server is up and running again?

Homepage is https://www.followtheboat.com/index.php (you have to add the index.php or else you’ll go to the old site).

Any help really appreciated as I’m not sure whether to start panicking yet!