Website is down (Somebody else's website)

Maybe the website you are trying to visit is restricted to certain countries other than yours or maybe there is something wrong with your ISP. The first thing you should do is to check whether the website is really down for everybody. Go to Downforeveryoneorjustme and enter the website's URL in the field (e.g. google.com) and press Enter.

If the website is up, you will be able to access it through a proxy server. Search for most popular and most secure proxy websites and try one of them.

If you use a router and you cannot load any website, probably the router itself is the issue. Maybe the Internet connection crashed and the router failed to re-connect or maybe it was something else that caused the router to stop working properly.

Restart the router by unplugging it from the power outlet (the easiest way), or by pressing the Power ON/OFF button (if available). Wait for 30 seconds to ensure all the power is gone and then plug it back in (or turn the power button on) again. After that, wait until the router reconnects to the Internet again.

If others can access the desired website (or your website) but you, there is a possibility that the hosting server of the website is blocking your IP address, or there is something wrong with your ISP's (Internet Service Provider) settings.

Some website owners do this to prevent users from certain countries/location from accessing the website, or to restrict the number of visits (e.g. You get kicked out if you visit the website more than 10 times per day).

Try to access the website through a proxy website. Famous proxy websites include hide.me, hidemyass.com, proxysite.com. If you are not sure how to use the proxy website, they include video tutorial for that purpose. Please note that this is a short-term solution to your problem.

To fix it long-term, contact your ISP first and then the server admins / hosting provider of the page you're trying to access to check why they are blocking you.

The hosts file enables you to add URLs of webpages you want to block, which will automatically be blocked in every single browser installed in your computer. Also, some viruses can modify the hosts file in order to prevent you from downloading an antivirus software which can find and remove the virus.
 
All you have to do to fix this issue is to open and modify the hosts file:

My Computer -> Local Disk (C:) -> Windows -> System32 -> drivers -> etc

Open it with Notepad (right-click the hosts file -> Open with -> select Notepad). In the hosts file you will see other addresses which serve as an example and which you MUSTN'T delete. If you find a link associated with the website you want to open or with an antivirus software, delete it and save the changes.

The hosts file enables you to add URLs of webpages you want to block, which will automatically be blocked in every single browser installed in your computer. Also, some viruses can modify the hosts file in order to prevent you from downloading an antivirus software which can find and remove the virus.
 
All you have to do to fix this issue is to open and modify the hosts file. To modify the hosts file:

1.  Open the Terminal.app by going into Applications -> Utilities -> Terminal.
   
   
2. Type the following line: sudo nano /private/etc/hosts (type your username and password when asked)
   
   
3. If you notice a URL of a websites you visit, or websites of antivirus software, delete them and press and hold Control + O to save the changes and Control + X to exit
   
   
4. Flush the DNS cache by entering the following line (depending on your OS version):
   
   
   • dscacheutil -flushcache - Mac OS X Snow Leopard (v10.6 through v10.6.8)
     
     
   • sudo killall -HUP mDNSResponder - Mac OS X Mavericks, Mountain Lion, and Lion (v10.9.5 and earlier)
     
     
   • sudo discoveryutil mdnsflushcache - Mac OS X Yosemite and later (v10.10 through v10.10.3)
     
     
   • sudo killall -HUP mDNSResponder - Mac OS X Yosemite and later (v10.10.4 or later)

Maybe a virus is preventing your browser from working properly or is slowing down your Internet speed and it seems that the website (or all websites) is down.

To learn how to scan for and remove viruses, check out the Viruses / Spywares / Malware solutions.

Maybe the issue is in the server. Corrupt memory chips or disk sectors are known to be responsible for a large number of website-related issues and as a result of that, your website is unable to work properly.

First of all, check the memory chips and the disk sectors. If everything appears fine, the website's code might be the problem.

The best way to fix it, if you are not 100% sure, is to hire a professional to do it instead of you.

Note: If you still decide to try to fix it by yourself, check out this article.