You didn't give a model number but I believe all their NVRs have a separate light for power, HD, and network. If the power LED is flashing, then you need to check the power supply with your DMM and make sure it's within spec.

Again model number! Does this NVR have a built-in power supply or an external brick? Even with it built-in, many of those have a separate power supply board inside that is easily replaced. I have a power supply board for a 16ch POE enabled unit in-stock.