We bought a 4CH MPEG-4 Dvr system with 4 IR cameras and cannot get it to work. The book is very vague, it says to install a HDD but it already comes with a 160 gb hard drive But we can't get it to work. Please help

List the brand and model.
If it has the option of purchasing without a HDD maybe it needs an initial set up. It wold need to know the size of the drive to calculate when it will need to overwrite old files. It maybe needs to be partitioned and formatted also. Look for a settings/setup mode to select on the DVR.

Make and model would be nice as well. It will save a lot of running around in the dark...