composer: Could not connect to packagist.org

My composer.json:

{
    "name": "laravel/laravel",
    "description": "The Laravel Framework.",
    "keywords": ["framework", "laravel"],
    "license": "MIT",
    "type": "project",
    "repositories": [
        {
             "type": "composer", 
             "url": "https://packagist.org"
        }
    ],
    "require": {
        "php": ">=5.6.4",
        "laravel/framework": "5.3.*",
        "laravelcollective/html": "^5.3.0"
    },
    "require-dev": {
        "fzaninotto/faker": "~1.4",
        "mockery/mockery": "0.9.*",
        "phpunit/phpunit": "~5.0",
        "symfony/css-selector": "3.1.*",
        "symfony/dom-crawler": "3.1.*"
    },
    "autoload": {
        "classmap": [
            "database"
        ],
        "psr-4": {
            "App\\": "app/"
        }
    },
    "autoload-dev": {
        "classmap": [
            "tests/TestCase.php"
        ]
    },
    "scripts": {
        "post-root-package-install": [
            "php -r \"file_exists('.env') || copy('.env.example', '.env');\""
        ],
        "post-create-project-cmd": [
            "php artisan key:generate"
        ],
        "post-install-cmd": [
            "Illuminate\\Foundation\\ComposerScripts::postInstall",
            "php artisan optimize"
        ],
        "post-update-cmd": [
            "Illuminate\\Foundation\\ComposerScripts::postUpdate",
            "php artisan optimize"
        ]
    },
    "config": {
        "preferred-install": "dist"
    }
}

Output of composer diagnose:

C:\xampp\htdocs\contetra>composer diagnose
Checking composer.json: OK
Checking platform settings: OK
Checking git settings: OK
Checking http connectivity to packagist: Warning: Accessing packagist.org over http which is an insecure protocol.
FAIL
[Composer\Downloader\TransportException] The "http://packagist.org/packages.json" file could not be downloaded: failed to open stream: A connection attempt failed because
not properly respond after a period of time, or established connection failed because connected host has failed to respond.

Checking https connectivity to packagist: FAIL
[Composer\Downloader\TransportException] The "https://packagist.org/packages.json" file could not be downloaded: failed to open stream: A connection attempt failed becaus
 not properly respond after a period of time, or established connection failed because connected host has failed to respond.

Checking HTTP proxy: FAIL
[Composer\Downloader\TransportException] The "https://packagist.org/packages.json" file could not be downloaded: failed to open stream: A connection attempt failed becaus
 not properly respond after a period of time, or established connection failed because connected host has failed to respond.

Checking HTTP proxy support for request_fulluri: FAIL
Unable to assess the situation, maybe packagist.org is down (The "http://packagist.org/packages.json" file could not be downloaded: failed to open stream: A connection at
connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond.
)
Checking HTTPS proxy support for request_fulluri: FAIL
Unable to assess the situation, maybe github is down (The "https://api.github.com/repos/Seldaek/jsonlint/zipball/1.0.0" file could not be downloaded: failed to open strea
ailed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond.
)
Checking github.com rate limit: FAIL
[Composer\Downloader\TransportException] The "https://api.github.com/rate_limit" file could not be downloaded: failed to open stream: A connection attempt failed because
ot properly respond after a period of time, or established connection failed because connected host has failed to respond.

Checking disk free space: OK
Checking pubkeys:
Tags Public Key Fingerprint: 57815BA2 7E54DC31 7ECC7CC5 573090D0  87719BA6 8F3BB723 4E5D42D0 84A14642
Dev Public Key Fingerprint: 4AC45767 E5EC2265 2F0C1167 CBBB8A2B  0C708369 153E328C AD90147D AFE50952
OK
Checking composer version:

  [Composer\Downloader\TransportException]
  The "https://getcomposer.org/versions" file could not be downloaded: failed to open stream: A connection attempt failed because the connected party did not properly res
   time, or established connection failed because connected host has failed to respond.


diagnose

I am using windows. Also, I am unable to open packagist.org site and getcomposer.org website too. PHP version is not the issue, as i am using the latest version.

What can i do to make composer work?