I do not always maintain PHP sites but when I do, I usually break them with upgrades. This time I upgraded Nginx 1.6 to 1.8 on a Debian Wheezy installation and had a set of WordPress sites returning empty responses. The issue can be resolved by adding
fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
or equivalent to your FastCGI conf. Where exactly, depends how you installed Nginx, or what distro you use. On Debian Wheezy with Dotdeb repo it goes into the
I really hope that one day I have no PHP installations to maintain.