*Urgent*: Need to fix htaccess file

My website is being launched today at a public event and something has gone wrong. It was working fine a couple of days ago so this is really mystifying.

I can access my site at https://gendercentre.com but I get blank screens when I try to access https://www.gendercentre.com and https://gendercentre.com/wp-admin

I’ve called my host and have been told that the DNS is fine and that my WP htaccess file must be missing some code. This is what the file currently has:

# Options -Indexes

# BEGIN WordPress

# END WordPress

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress

Please help. I’m desperate!