Website is down (I use Hostgator)

A low PHP Memory Limit is one of the factors responsible for the 500 Internal Server Error. To fix it:

1.  Open the WordPress root directory in FileZilla (click here if you don't know how to install and configure it) or your preferred FTP client (a software which uses the FTP- File Transfer Protocol to transfer files to and from a remote computer).
   
   
2. Locate the wp-config.php file, download it and open it in Notepad or other text editor (right-click on the file -> Open with -> Select a text editor)
   
   
3. Add the following code and save the file:

   define('WP_MEMORY_LIMIT', '64M');

4. Re-upload it to wordpress (by selecting the upload option) and overwrite the original file
   
   
5. Try opening your website in a web browser

Note: If this didn't fix the error, remove the above-mentioned code from the wp-config.php file, save it, and re-upload it to the root directory.

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)

If your website is down, run a test to determine if there is an issue with the IP address or not.

To check if there is an issue with the IP address:

Go to network-tools.com, select ping, enter your website URL and check if it returns the correct IP address that belongs to the server where your website is hosted (refer to the documentation that your hosting company sent to you when you first signed up to it).


Also, you can do this test through CMD/Terminal:

Windows:

1. Type cmd in the start menu search box
   
   
2. Type the following using your domain and press Enter: ping www.yourdomain.com (e.g. ping www.youtube.com)
   
   

If the server is alive and reachable, then the result will be something like this:

Reply from IPADDRESSHERE (e.g. reply from 92.52.106.33:) bytes=32 time=12ms TTL=53

This line should repeat four times.

Mac OS:

1. Go to Applications -> Utilities -> Terminal
   
   
2. Type ping www.yourdomain.com (e.g. ping www.youtube.com)

If the server is alive and reachable, then the result will be something like this:

Reply from IPADDRESSHERE (e.g. reply from 92.52.106.33:) bytes=32 time=12ms TTL=53

The will repeat indefinitely, as long as you don't press and hold Control + C

Check if the IP address you got from the test matches with the one from your hosting documentation. If it does not match, this indicates that the domain name could have expired.
If you receive something like unknown host, then it’s definitely a domain name issue.

In a situation like this, use a website such as Who.is to verify the domain registration details. You will find out when it expired, who owns it at the moment and where it is registered. Then you can contact the domain registrar to reclaim the domain.

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.

If your website is hosted by Hostgator and you experience issues you couldn't resolve by yourself, contact their support staff, who will help you resolve the issue and they are available 24/7 for you.

Contact them on:

• Toll Free: (866) 964 - 2867
• Local: (713) 574 - 5287
• International: 00+1-713-574-5287
• Fax (Billing): (281) 476 - 7800
• Fax (Abuse): (281) 476 - 7801

or via their live chat service

There are two possible reasons for the 401 Unauthorized error. One of them is a misspelled URL, and the other reason is incorrect credentials (username and password).

Firstly, check if you have typed the URL correctly, and then check your login details.

Note: If both, the URL and the credentials are correct and you still see this error, report the issue to the webmaster.

Most websites use resources on other servers. This includes CDN-hosted files, database servers, or remotely-hosted APIs such as those for Google Maps, YouTube, Twitter, advertising services, etc.

If one of those is down, that can cause your website to go down as well. Before taking any other action, make sure that every other resource you use on your website is available.