Upgrade Issue – “The page isn’t redirecting properly”

I have just upgraded from 2.3 to 2.5.1. Seemed to go smooth. I can get into the back end admin stuff if I go directly by URL /wp-admin/index.php, but when I try to getinto the front end of my blog viewable to my users, I get the following error message in my browser.
I don’t know what file got affected to have this happen.

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.

* This problem can sometimes be caused by disabling or refusing to accept
cookies.