If you have a wired kit DVR/NVR such as X4/X5 and the camera shows as Disconnected or Disabled in Menu > System Information, you can follow the steps below to troubleshoot the issue:
First, make sure that the power supply for your DVR/NVR is sufficient. If it is, but the issue persists, try the following methods:
Check if the firmware of your system is up to date. You can do this by navigating to Device Management > Advanced Settings > Maintenance > Upgrade.
Unplug and plug the power adapter back in. Then, click on the Shutdown button and choose the Reboot button to restart your system.
You may also try restoring the system to default settings by going to Device Management > Advanced Settings > Maintenance > Default.
If the issue persists only with some of the cameras, you can further troubleshoot by swapping the power cable and port with a functioning camera to see if the problematic camera starts working.