The program seems to have changed entirely, so I can't comment on exact code. However, from what I remember, the ball bounced off the top paddle just fine. The problem was that the ball also bounced off the top edge. When the ball got "stuck", what was happening was the ball bounced off the top edge of the screen, then bounced back and forth as it was sandwiched between the top edge of the screen and the top edge of the top paddle.
The student needs to change the code so when the ball touches the top edge of the screen, the player wins (or the ball resets, or something other than bouncing back down).