I seem to always have trouble logging in. When I try to log in, I get a message saying something like welcome back or whatever and get redirected. That all seems normal. But, I don't get logged in. It happens everyday but after a ton of tries, I get logged in. Very strange.
Not a forum specific answer, but have you tried clearing your browser history and cache? I have had, not on this site but others, previous history and cache interfere with log-ins before.