If all cameras are connected to DVR/NVR with cables and recorder is connected to a monitor with a cable, one or several cameras show no live video on monitor, but others are working fine.
1. connect camera C1 to channel A1 with working cable B2 to confirm if it is cable B1's proble.
2. Connect camera C1 to working channel A2 with working cable B2 to confirm if it is camera C1's problem.
3. Connect working camera B2 to channle A1 with working cale B2 to confirm if it is channel port A1's problem.
Please confirm which part is broken, camera, cable, or channel port so that we can give you the correct replacement.
You can also go to main menu----info----BPS to check if camera has connected to system.
You can also use hands to cover the front of camera. If you can see infrared lights turns on with red lights, cameras are on.
If the camera is not on, connect adapter to the camera directly without 1/4 spliter to have a try.