If you think it's a problem with the dns you can try the following.
Open up cmd. I don't know which version you have so either go to Run > type in cmd or search in the Vista search box at the Start menu. For Vista you'll need to right-click and go to Run as Admin.
Type in:
ipconfig/flushdns
Other things you can also do is...
ipconfig/release
ipconfig/renew
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