Why I can use rviz to show the depth points (Kinect Xbox 360)

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Dear All. Today |I buy a xbox360 Kinect, install it on ubuntu 11.04 ros electric. Everything is fine. But when I run
roslaunch openni_launch openni.launch rosrun rviz rviz I can see the rgb image. But I can not see the depth image. I add one pointcloud2.
Set the Fixed Frame (top left of rviz window) to /camera_depth_optical_frame.

Add a PointCloud2 display, and set the topic to /camera/depth/points. I can not see any information. How to solve the problem. I am sure the hardware s good,and it is normally from another computer.Only it is not worked for my laptop and desktop. Linux 11.04, ros electric. I also try the kinet+mouse demo. it works. Without depth information, I cannot try the roboearth package. Thanks any help.