No one seems to have answered which I'm surprised about.
I assume you are using IE6? If so, try and lower your privacy settings slightly, on the top menu bar go to Tools and click on it, go down to Internet settings and click on it. Along the tabs I think there's one marked Privacy, if you click on it you should see a slider bar on the left, try lowering it to medium and try again. That will allow cookies required to enter those sites.
Come back here if you still have problems.