How To Clear Your DNS Cache

HTML 404 error codes 

Below One of the reason website not opening.

Overview

Your DNS cache stores locations (IP addresses) of webservers that contain pages which you have recently viewed. If the location of the web server changes before the entry in your DNS cache updates, you will be unable to access the site. If you encounter a large number of HTML 404 error codes, you may need to clear your DNS cache. Once you clear your DNS cache, your computer will query nameservers for the new DNS information.

How to clear your DNS cache

The following methods allow you to remove old and inaccurate DNS information that may result in 404 errors.

Windows® XP, 2000, or Vista®

1. Click the Start button.
2. On the Start menu, click Run....
   • If you do not see the Run command in Vista, enter "run" in the Search bar.
3. Type the following in the Run text box: ipconfig /flushdns

MacOS® 10.7

1. Click Applications.
2. Click Utilities.
3. Double-click the Terminal application.
4. Type the following: sudo killall -HUP mDNSResponder
   • Warning: To run this command, you will need to know the computer's Admin account password.

MacOS® 10.5 and 10.6

1. Click Applications.
2. Click Utilities.
3. Double-click the Terminal application.
4. Type the following: dscacheutil -flushcache