Not all Internet problems can be blamed on yourself, more often, they are the result of a mischief from your Internet service provider. When some specific websites stop working or is having difficulties, your Internet are probably fine. It’s probably problems from your ISP’s DNS.
Now, What is DNS
In the most simple term, it is a entity that changes your HOST Name(www.example.com to IP ADDRESS(123.11.66.91) and vice versa.
When connecting on websites, the computer sends a request to a DNS server and the server returns the IP address for the website. For example, when trying to connect to google.com, the computer sends a request to the DNS server asking for the IP of google.com. The DNS server will return 173.194.32.104, which is Google’s IP address. The Internet browser then use that IP address to connect to the website.
The problem? Some DNS servers from ISPs have a slow response under heavy load and will delay the time to load a web page. It is also frequent that the DNS are out of sync with the root server, and you might have to wait hours before it gets synced with the right information again. This happens often when a website have their IP changed and many DNS servers around the world haven’t been updated yet.
The solution? You can move to free alternative DNS servers like  OpenDNS or  Google Public DNS servers.
Instructions are supplied on their websites.
The setup varies depending on your operating system and can even be set up on your router if it is supported.
How to set up Google’s Public DNS on Windows 7
On Windows 7, go to Control Panel> Network and Internet> Network and Sharing center> Select your Internet connection.
In the dialog, click properties. Then, select Internet Protocol version 4, and click properties and edit the configuration to those in the picture.
Google’s DNS server addresses are:
8.8.8.8 and  8.8.4.4
- 208.67.222.222 (resolver1.opendns.com)
- 208.67.220.220 (resolver2.opendns.com)
- 208.67.222.220
- 208.67.220.222
Click OK and you’re done! Happy surfing!