Hello Aspirant! If you are not able to register yourself in JEE Advanced then it might be because you have not qualified the expected cutoff marks for the same. Or if the window isn't loading then it might be due to some server problem as several students are registering for the same or you might have a poor internet connection. No need to worry if window isn't loading. Try again after a few hours and it will be solved. Else, check the cutoff and see if you've cleared it or not.