First, try adding fastcgi_index index.php; as outlined on the linked page, and reload nginx.
I gather you're using Cloudflare. If it is presently enabled, can you try adding $CFG->reverseproxy = true; in config.php? (Process is similar to as Leon described above in relation to default homepage).
Sorry, but what do you mean by 'if i disconnect, i am able to see the Homepage'?