The screen is flickering on and off on the or screen is black and is connected to the NVR HDMI port and it just kept flickering on and off and barely see the screen. Once I switch over to VGA port it works fine.

 The issue that you're experiencing could be one of the reasons below:

•  Display output settings in the NVR, and compatibility problem with your TV/Monitor. Below you will find a link to view our step-by-step Video Tutorial ( jump to minute 25:37) and/or download the USER MANUAL for this model (refer to page 108) 
• HDMI may not be connected properly. please make sure it is pushed in firmly
• Faulty HDMI Cable. Try replacing the HDMI Cable with a new one

If the problem persists, it could be that the NVR has a faulty HDMI port please CONTACT US and we will help resolve this issue.