Domain Name Servers (DNS) map domain names (such as Google.com) to IP addresses. The 'memory' of all the DNS lookups your computer has performed is called the 'DNS cache'. Sometimes, for various reasons, the cache becomes corrupt or out-of-date, so it's necessary to flush your DNS cache.
Here are some general instructions for clearing your cache based on the operating system:
Mac OS X
Flush the DNS Cache [Mac OS X 10.4 and older]
Open a new terminal window.
You can do this by simultaneously pressing the command & spacebar to bring up the spotlight search and typing in 'terminal', then clicking on the terminal program in the search window.
Type 'lookupd -flushcache' in your terminal window
Press Enter
Flush DNS Cache [Mac OS X Leopard 10.5 and newer]
Open a new terminal window.
You can do this by simultaneously pressing the command & spacebar to bring up the spotlight search and typing in 'terminal', then clicking on the terminal program in the search window.
Type 'dscacheutil -flushcache' in your terminal window.
Press Enter
Windows
Open the command prompt. The command to flush DNS needs to be entered in the command prompt. Accessing the command prompt is slightly different depending on which version of Windows you are running:
Windows 8 - Press the Windows key + X and select “Command Prompt (Administrator)”.
Windows 7/Vista - Click the Start menu and enter “cmd” into the Search field. Right-click on Command Prompt and select “Run As Administrator”.
Use the DNS flush command. Type ipconfig /flushdns and press Enter. A message will appear stating, “Windows IP configuration successfully flushed the DNS Resolver Cache”.
Exit the command prompt. Type exit and press Enter. This will close the command prompt.