Motion blur hasn't worked since ive gotten after effects

Can you be more specific and post screenshots? What are you trying to apply motion blur to, footage that's playing back or a layer that's been keyframed? The easiest way to show how motion blur works is to create a simple shape and keyframe it going from one side of your frame to another. In recent versions of After Effects simply turning on the layer's motion blur switch will now enable it for the entire comp. In Previous versions you had to also manually enable the Motion Blur switch near the top of the Timeline panel (on the right of the search bar). If you position your two keyframes close together so the motion is fast, you should see motion blur. See the attached GIF showing what I describe above. If you can be more specific with what you're trying to do and what isn't working, then we can provide more specific details to help solve your problem.