First of check to make sure that your BIOS is properly seeing the DVD drive.
Also some DVD drives if they are connected with another optical drive on the same IDE channel, have to be slave, or was it master, no it was slave.
Forgive me I just woke up

Anyway after you know your BIOS sees it, make sure Win sees the drive, if it does and you still cannot get Power DVD to see it, well I would then reinstall the program from the DVD drive.
Can't think of anything else at the moment, brain still too foggy.