I do some work with DVRs and there is no standard file system and the company I do this work on has a different proprietary system (there is no file system on these!) on each DVR. To access the content took about 5 million dollars and a world of programmers.
In short, unless you are inside and working for the company no one will help you here.
Try disk manager to see if you can re-cycle the drive and remember that newer set top DVRs now use modified drives to prevent use in PCs.
I have a hard drive that was removed from a Motorola DVR. The HD is a Seagate 160 GB. I connected the SATA drive to my computer. When I went into My Computer, the drive isn't shown. I went into the Control Panel and it's shown. I called the Seagate tech support and their conclusion is that there is some other software on the drive than Windows. Plus, they don't support any 3rd party situations. So, how do I access a hard drive that doesn't have Windows on it?