The cameras have already been configured with IP addresses and passwords from the old NVR.
Did you match the camera IP addresses to the IP addresses of the PoE channels on the new NVR?
Do you know the individual camera IP addresses so you know what NVR PoE port to connect them to?
Did you use the same NVR password on the new NVR? By default, in Plug&Play mode, the NVR will apply its own password to the NVR.
So the cameras will probably have the old NVR password.
Check which cameras have which IP address by connecting a PC to an unused NVR PoE port and looking at what SADP finds.
Unplug one camera and see which one disappears on a SADP refresh.
Then plug the cameras in the corresponding NVR PoE port to match the IP address of the port.
**edit** This all assumes the (unspecified) NVR and (unspecified) cameras are Hikvision models.