c. The NVR boots up normally, but the monitor screen is black. What might be the problem?

Answer:

1. It is possible that the monitor does not support the resolution that the NVR has been set to. On the remote control, long press the stop button to restore the output resolution of the NVR.
2. One of the NVR’s output ports may be damaged. Try connecting the monitor to another video display output port (VGA or HDMI) to see if it works on the other port.