gregplus,
There are 2 sets of test media that come with your kit CD and DVD.
In windows the CD tests require the CD media and the DVD tests require the DVD media. In DOS it will test whatever is inserted into the drive.
If you have the proper test media inserted for the selected tests then either the media is bad or the optical drive does not recognize it. You can test this by choosing the CD tests and inserting a CD that contains data (one other than the PC-Doctor media). It is conceivable that you were given bad test media, this will confirm whether it is good or bad.
-Fred