You can see in My Computer if they are empty (0 bytes) or not (>0 bytes).
http://filext.com/file-extension/dng mentions 2 possible sources:
File type: Digital Negative Format
Company: Adobe Systems Incorporated
Dungeon File (created by ID software)
Does this ring a bell?
In what folder are these files located?
On my harddrive local disc I have dozens of DNG files that I cannot open does this mean that they are empty or do I need a special program to open them.