Have you tried pressing the magic f5 button? Also, try and see if you can pop in your XP or Vista disc and repair the system if you have other problems.
If that doesn't work, try another browser (Mozilla instead of IE or IE instead of Mozilla).
Also, have you tried Control Panel - Internet Settings - Security (or something like that, mine is in German
) and have a look if you have put it in untrustworthy sites by accident.
Could also be a firewall problem (there was another thread about ppl having to download things when they want to come here). Which one are you using? If it's one where you can see what is blocked (like Zone Alarm), try and unblock the right one.