Under these circumstances, the problem is most often with the local browser or DNS caching either on the local workstation, your local ISP or your ISPs upstream provider.
To clear up any local workstation issues, you may wish to try and close down all copies of your browser. If using Windows, you can also go to Control Panel, Internet Options. From there you can delete all your cookies, files, offline files. It may also be helpful to reboot your workstation. All of these things are intended to ensure that your browser and network caches are cleared.
You can clear the DNS cache on your local workstation by closing all browser windows, opening a command prompt (Start-Run-cmd), and typing "ipconfig /flushdns". The program should respond "successfully flushed the DNS resolver cache"
To verify the global DNS settings, you may wish to try:
http://www.checkdns.net (perform a "quick check" by entering your domain name into the appropriate field and clicking on the "submit" button.)
If after doing the above, you are still having trouble, you can try to "ping" the server. To do this, open up a command-line prompt and perform ping and a trace-route test to your site by entering in:
(where "YourDomain.com" is your full domain name)
If any of the ping or trace route tests fail, the next step is is usually to contact your ISP and ask them to look into this. If you are unsure of what these tests should show, you can forward the results to us and we can advise you on the next step.