Generally, you should remove power from the device, then press and hold the button. While holding the button down, apply power to the device. Continue holding the button down for 15 to 30 seconds, then release. Generally, this will reset the device to factory defaults.
If that is unsuccessful, then take a paper clip and untwist it, and bend it into a 'U' shape. With the power removed, insert it into the holes at J10 and then apply power. After 15 to 30 seconds, remove power, remove the paper clip, and re-apply power.
One of those two should do it, if not, can you attach a USB keyboard and interrupt the BIOS/CFE/bootloader? I'm not even certain if that's possible with these NVR units.
If that is unsuccessful, then take a paper clip and untwist it, and bend it into a 'U' shape. With the power removed, insert it into the holes at J10 and then apply power. After 15 to 30 seconds, remove power, remove the paper clip, and re-apply power.
One of those two should do it, if not, can you attach a USB keyboard and interrupt the BIOS/CFE/bootloader? I'm not even certain if that's possible with these NVR units.