nginx "file not found" with index.php

hello,
I installed nginx in my ubuntu machine, php and fcgiwrap.
I made many modifies to config files to resolv many issues
(403, 404, 502) and now when I open "localhost/index.php"
the error message is "file not found".
with "localhost/index.html" it works.

with tail -f /var/log/nginx/error.log
this is the error: 2016/02/25 18:00:53 [error] 1082#0: *4 FastCGI sent in stderr: "Primary script unknown" while reading response header from upstream, client: 127.0.0.1, server: localhost, request: "GET / HTTP/1.1", upstream: "fastcgi://127.0.0.1:9000", host: "localhost"

and if I make sudo netstat -alnp | grep cgi
it says: unix 2 [ ACC ] STREAM LISTENING 13560 918/fcgiwrap /var/run/fcgiwrap.socket

may you help me please?
thanks. bye.