You can remove the hard drive and attempt to access it on a PC, that's the only hope you have for saving the contents. Results vary, if the drive is intact it's certainly possible but not an easy task. These units use proprietary formatting, and some even encrypt the video files. Chances are the drive has Linux type formatting.
The message means that the device is seeing a blank disc, or that the hard drive is unformatted. Sounds like you are screwed. This is why I burn everything on my DVR to DVD for safe keeping.