Click Start> Run> type in CMD tap enter key
At the prompt: Copy/Paste: ipconfig /flushdns
If you are typing this in, note the space between the g /f
It needs to be there.

Why flush DNS cache?

http://www.updatexp.com/dns-windows-xp.html

When you visit a website, Windows XP tries to speed things up by placing the DNS information about that site, into a DNS cache on your PC.
This is OK until there are problems with the network, DNS server or even the website!

You see the DNS Windows XP cache stores BOTH negative and positive entries. The positive entries are those that the DNS lookup was successful and you could connect to the website.

If you have a bad guy in your DNS cache, that can hijack your web browser.