Login OK, but 404! Where is everything?

I keep getting a 404 / "Ack! We can't find that page" whenever I login. The only way I can tell that I'm logged in is because there is a "Logout" button as well as "Find friends" and "Settings"

I did a password change as I read on here that someone else had the same problem and that fixed it. But I'm not having any luck. Any ideas?