What do you do when you have a test in less than a week but your brain shuts down on you??

I find that just reading something as a way to study does not engrain itself in your brain nearly as much as writing down the pertinent points.
When you write something it occupies a place in your mind that is more easily recalled than just reading it.
When you become distracted, step away from it and do something else to clear your mind.
Without full focus, you will not retain. Better to have shorter periods of clear focus than long periods of distracted focus.
Good luck!