It is possible the internal power supply has failed, this could've blown other components on the main pcb. You could take a chance and replace the power supply.
@theworldisacube disconnect your NVR from the electrical supply and remove the lid (this will invalidate any warranty you have). The attached picture should
be the inside of your NVR and I've marked the PSU. The model number will be on the white label stuck on the psu. search the internet and if you find one make sure it is exactly the same model.
replacing the PSU does not guarantee the NVR will work,