Clues=0
I'd start by assuming a browser problem, and reinstall/repair it. How (or if) you can do that depends on what you're using and what OS. Check add/remove programs and see if Microsoft Internet Explorer is listed - if it is, select it and hit add/remove. It'll give you a couple options, select "repair".
If that isn't it, some spyware garbage can give your browser indigestion too - drop by
http://www.lsfileserv.com/index.html and grab a copy of ad-aware and run it. Even if it doesn't fix the problem, you probably have onflow or some other garbage you can do without. It'll remove it.
After that, I'd try the Windows update site, and then reinstalling Windows (over the current install - not a format). I haven't got a clue what the problem is, but if none of that fixes it you're probably just screwed.