Linux – High Load Average But CPU And Memory Are Not Used NGINX

First of all I want to explain what I am using the server for.

This server is used to deliver downloadable files. Specially video games which I upload to the server and then users can download it through form action. Below is the link to the source where the download file is requested.

The problem I am facing is that I have Intel Core i7 8 Cores 12 GB Ram dedicated server. And whenever I let my users download files through the server it starts generating high load average and the server is then unable to fetch downloads through the PHP pages that I created it for.

I have also attached my Nginx.conf and other screenshots so do check them out.
And one more thing: whenever I restart my nginx its gets ultra fast despite the load average but then again slows down after a minute.

You can check here this is the source where the download file is requested

worldofpcgames.net/fairy-fencer-f-advent-dark-force-free-download/

HERE IS MY NGINX->

user nginx;
worker_processes 8;
worker_rlimit_nofile 5000;
error_log /var/log/nginx/error.log;
pid /run/nginx.pid;

# Load dynamic modules. See /usr/share/nginx/README.dynamic.
include /usr/share/nginx/modules/*.conf;

events {
    worker_connections 3000;
    use epoll;
    multi_accept on;
}

http {
    log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
                      '$status $body_bytes_sent "$http_referer" '
                      '"$http_user_agent" "$http_x_forwarded_for"';

    access_log  /var/log/nginx/access.log  main;

    sendfile            on;
    tcp_nopush          on;
    tcp_nodelay         on;
    keepalive_timeout   65;
    types_hash_max_size 2048;

    include             /etc/nginx/mime.types;
    default_type        application/octet-stream;

    # Load modular configuration files from the /etc/nginx/conf.d directory.
    # See http://nginx.org/en/docs/ngx_core_module.html#include
    # for more information.
    include /etc/nginx/conf.d/*.conf;

    server {
        listen       80 default_server;
        listen       [::]:80 default_server;
        server_name  _;
        root         /mnt/www/html;
    index index.php;
        # Load configuration files for the default server block.
        include /etc/nginx/default.d/*.conf;

        location / {
        try_files $uri $uri/ =404;
    }
    error_page 404 /404.html;
    error_page 500 502 503 504 /50x.html;
    location = /50x.html {
        root /usr/share/nginx/html;
    }


    location ~ \.php$ {
        try_files $uri =404;
        fastcgi_pass unix:/var/run/php-fpm/php-fpm.sock;
        fastcgi_index index.php;
        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
        include fastcgi_params;
    }
        location /protected {
            root /mnt/www/html;
            secure_link $arg_md5,$arg_expires;
            secure_link_md5 "$secure_link_expires$uri$remote_addr enigma";

            if ($secure_link = "") { return 403; }
            if ($secure_link = "0") { return 410; }
    error_page 403 /blocked.html;
        }
}

# Settings for a TLS enabled server.
#
#    server {
#        listen       443 ssl http2 default_server;
#        listen       [::]:443 ssl http2 default_server;
#        server_name  _;
#        root         /usr/share/nginx/html;
#
#        ssl_certificate "/etc/pki/nginx/server.crt";
#        ssl_certificate_key "/etc/pki/nginx/private/server.key";
#        ssl_session_cache shared:SSL:1m;
#        ssl_session_timeout  10m;
#        ssl_ciphers HIGH:!aNULL:!MD5;
#        ssl_prefer_server_ciphers on;
#
#        # Load configuration files for the default server block.
#        include /etc/nginx/default.d/*.conf;
#
#        location / {
#        }
#
#        error_page 404 /404.html;
#            location = /40x.html {
#        }
#
#        error_page 500 502 503 504 /50x.html;
#            location = /50x.html {
#        }
#    }

}

And HERE IS THE NGINX error log ->

And one more thing i havent configured my PHP or Mysql at all. I just installed them and did the basic settings such as changed the user and owner group to nginx. and listen

HERE are the screenshot of TOP->

atop -c

And i am on Centos7
So please help me out

Sorry here is the nginx.conf couldn't link above because I don't have reputation points
https://drive.google.com/open?id=0ByamFYoTQ6KRRFpnUWJ3VGNxUEE