wp-admin redirection

I tried to upgrade to WP 3.0 and since then I have not been able to login to WordPress. I get this message when I go to the wp-admin page:

The page isn’t redirecting properly

Firefox has detected that the server is redirecting the request for this address in a way that will never complete.

I have tried to restore my database from prior to the upgrade, installed a fresh install of WordPress 2.9.2 and even changed the name of the .htaccess file in my root folder. Still, I cannot login.

Any suggestions? What should I do?