Have you tried using a different browser?
If you're using Internet Explorer (WHY? WHY? WHY?) try Firefox:
http://www.mozilla.com/en-US/firefox/new/
If you're already using Firefox, either try Internet Explorer (because it's almost certainly immediately available to you to try) or, far better, Chrome:
http://www.google.com/chrome
If you get the problem across several browsers, it suggests that it might be related to the site which you're trying to access, rather than to any problem with your computer.
Chris