If you have not tried connect DVR/NVR to VGA monitor yet, please have a try to check if you can see image via VGA first.
If you can see image with VGA cable to your monitor but no image on HD TV with HDMI cable connection, please try methods below.
1. Make sure your TV is in HDMI mode, not VGA mode nor BNC mode. You can the remote of TV to switch mode.
2. Change DVR's video output resolution to a lower one 1024*768. You need try every reoslution on the list. This is the most effective way to solve this issue,and you must have a try.
3. Change a HDMI cable to have a try.
4.Change another HD TV if you can.
5.Restore system to factory default.