I've had this happen to me before. It just sits there as if waiting for you to do something while its trying to load, right?
Is there another error messege besides from what you are seeing? Sometimes, you could have accidently edited your default user as KDE starts up. To change it, you can access the login screen, and type in "root" as username. then your root password as your password. That will bypass your problem, and then load KDE. Then, you can edit your default profile to where it will work again..If you don't know how, I can explain when we get to that bridge..