Wordpress category links are not working and sometimes PHP gives a blank page on an Nginx server

I just configured a new server to move my website. After I migrated, everything works fine except for category links. If we visit a category, it will give a 404 error. Page permalinks are working fine! What might be the problem? One website gives this problem immediately, the other after sometime. Sometimes even the posts go missing.

Sometimes I even get a problem of having blank pages for php files.

The nginx conf :

    server {
            listen   80;


            root /var/www/androidgadgematic;
            index index.php index.html index.htm;

            server_name androidgadgematic.com www.androidgadgematic.com;

            location / {
                try_files $uri $uri/ /index.php?q=$uri&$args;
            }

            location ~* .(jpg|jpeg|png|gif|ico|css|js)$ {
                expires 10d;
            }

            error_page 404 /404.html;
            error_page 500 502 503 504 /50x.html;

            location = /50x.html {
                  root /usr/share/nginx/www;
           }


            location ~ /\. {
                    deny all;
                    access_log off;
                    log_not_found off;
            }

            location ~ /nginx.conf {
                    deny all;
                    log_not_found off;
                    access_log off;
            }

            location ~ ^/feed/(.+)\.html$ {
                    if ($args != '') {
                    rewrite ^(.*) $1? permanent;
                    }
            }

            # pass the PHP scripts to FastCGI server listening on 127.0.0.1:9000
            location ~ \.php$ {
                    try_files $uri =404;
                    fastcgi_pass unix:/var/run/php5-fpm.sock;
                    fastcgi_index index.php;
                    include fastcgi.conf;
            }

            include /var/www/androidgadgematic/nginx.conf;
            location ~ "\.pagespeed\.([a-z]\.)?[a-z]{2}\.[^.]{10}\.[^.]+" { add_header "" ""; }
            location ~ "^/ngx_pagespeed_static/" { }
            location ~ "^/ngx_pagespeed_beacon$" { }
            location /ngx_pagespeed_statistics { allow 127.0.0.1; deny all; }
            location /ngx_pagespeed_global_statistics { allow 127.0.0.1; deny all; }
            location /ngx_pagespeed_message { allow 127.0.0.1; deny all; }
            location /pagespeed_console { allow 127.0.0.1; deny all; }

            location ^~ /wp-login.php {
                    auth_basic            "Restricted Area: WordPress";
                    auth_basic_user_file  /var/www/.htpasswd;
                    try_files $uri =404;
                    #fastcgi_pass 127.0.0.1:9000;
                    fastcgi_pass unix:/var/run/php5-fpm.sock;
                    fastcgi_index index.php;
                    include fastcgi.conf;
            }

    }

PS : Even the wp-admin gives 404

fastcgi.conf:

	fastcgi_param  SCRIPT_FILENAME    $document_root$fastcgi_script_name;
	fastcgi_param  QUERY_STRING       $query_string;
	fastcgi_param  REQUEST_METHOD     $request_method;
	fastcgi_param  CONTENT_TYPE       $content_type;
	fastcgi_param  CONTENT_LENGTH     $content_length;

	fastcgi_param  SCRIPT_NAME        $fastcgi_script_name;
	fastcgi_param  REQUEST_URI        $request_uri;
	fastcgi_param  DOCUMENT_URI       $document_uri;
	fastcgi_param  DOCUMENT_ROOT      $document_root;
	fastcgi_param  SERVER_PROTOCOL    $server_protocol;
	fastcgi_param  HTTPS              $https if_not_empty;

	fastcgi_param  GATEWAY_INTERFACE  CGI/1.1;
	fastcgi_param  SERVER_SOFTWARE    nginx/$nginx_version;

	fastcgi_param  REMOTE_ADDR        $remote_addr;
	fastcgi_param  REMOTE_PORT        $remote_port;
	fastcgi_param  SERVER_ADDR        $server_addr;
	fastcgi_param  SERVER_PORT        $server_port;
	fastcgi_param  SERVER_NAME        $server_name;

	# PHP only, required if PHP was built with --enable-force-cgi-redirect
	fastcgi_param  REDIRECT_STATUS    200;

PS : I downloaded and compiled Nginx from source to install page speed. Might this be the problem?