If you have problems logging in to Gmail, don’t panic. You might get a message in your browser saying something like “Gmail timed out” even when you’re able to access other pages (and ping your Gmail account via GoogleTalk, for example.) You may find you get this error even in different browsers, indicating it’s not a cache error.
The best way to resolve this is to try rebooting. That fixed it for me, and it should for you.