If it is while you are waiting for the ball to come back down its because your timer is set too low. Turn it up to 30 or so seconds and it should do it.
Mine goes dim sometimes like it timed out...but never completely out
Posted from my CrackBerry at wapforums.crackberry.com
Also check to make sure you didn't just go from a bright environment to a dim environment. I found out last week the BlackBerry auto adjusts it screen brightness depending on how bright the environment is.
