If the Power DVD is part of a bundle that came with the computer and you no longer have the registration number you will need to obtain another number by purchasing the license again from the website.
Nevertheless, the device not found error is not from this lack of registration. In the Control Panel, find the CD drive and right click on it and select Delete. The ensuing dialogue box will ask you to verify that you are removing the device. Select OK and proceed to restart the computer. The device will be installed upon detection when the operating system restarts. The device drivers will be install anew.
Hope this helps.
Chris
September 2006