Sounds like a problem with your cookies. Go into the kitchen and eat more, chocolate chip preferably.
And now onto the serious reply!
First clear your cookies, do this by going tools, options, then click on delete cookies. Then go to the privacy tab, click on advanced and make sure that third party cookies are either set to 'allow' or 'prompt' (personally I use prompt because then the pain in the arse ad banners and such can't save cookies on my system), then click on sites and make sure that none of the different URLs for GR are blocked, then try logging in.
Sam