But the system is also making a "Dii-Dii-Dii- Di-Di" sound when it is turned on, which I just ready means the HDD is either not working or needs to be initialised (which can only be done once I login....).
Yes, maybe been removed even? The (lack of) screws underneath would be a giveaway.
Is it possible that the system is not powering the camera's up because the HDD hasn't initialised? Or do you need to log into the unit after powering it on, before the camera's will initialise?
No, the cameras should normally at least light up the LEDs on the PoE ports.
it has 2 plugs on the camera - an ethernet cable that was plugged in, and a circular plug which, after checking out the online specs for the camera, it is the power cord/plug. This power cord/plug was not connected to anything
That's normal when the cameras are power by a PoE switch or NVR.
I assume the previous owner had a PoE hub/switch that all the camera's connected to, then connected from that into the NVR. The whole system was disconnected when they left, so I am guessing that they took the PoE switch. Does that sound right?
That's certainly a possibility. It's not mandatory to use the built-in PoE ports of the NVR.
The PoE channels can be manually configured to use LAN IP addresses with the cameras on an external PoE switch.
Which brings me to a possible hypothesis that might explain what you are seeing :
I just experimented with a DS-7604NI-K1/4P
Configured one of the PoE channels to connect to a camera on the LAN as opposed to one of the 192.168.254.x PoE port addresses.
The NVR connects OK to the LAN-connected camera, and a camera plugged in to the corresponding PoE port gets power - both LEDs come on.
I did the same on a DS-7816N-E2/8P NVR. This is much the same hardware series as your DS7604NI-E1/4p
When connecting to the PoE port that corresponds to a channel which the LAN-connected camera is connected to, the camera does not receive power, and the LEDs stay off.
So the way that channel has been configured, to connect to a LAN-connected camera, disables the physical PoE port.
So if the previous owner had the cameras on an external PoE switch and the NVR is configured to connect to what would then be LAN-connected cameras, maybe the ports are all disabled.
I think it's a plausible theory.
So, a suggestion:
Get hold of a 12v power supply to connect to the accessible camera.
Connect the camera ethernet cable in to a router port if one is available, so it's on the LAN.
Find the camera with SADP, check out the firmware version, and with luck it may be old enough to have the backdoor vulnerability such that the password can be extracted.
The NVR will be able to be reset to defaults by applying the same firmware version as is currently installed using the Hikvision
tftp updater.
It's easy enough to do.
The same method can also be used for the cameras.
If the method above doesn't work, the tftp updater will work OK, and we can help with the how-to.