A firmware update was recently released for the NVR6XX-4KS2 series devices.
Information, instructions, and download links can be found Here
Troubleshoot/NVR/System Does Not Boot
From Dahua Wiki
System does not boot
- Disconnect, reconnect power and video cables to system.
- Disconnect HDD and boot system. If system boots without HDD, then HDD has failed or is not compatible.
There are following possibilities:
- If Input power is not correct then switch input power.
- If Power connection is not correct then switch power connection.
- If Power switch button is damaged then replace power switch.
- If Program upgrade is wrong then install correct program upgrade or send to RMA.
- If HDD malfunction or something wrong with HDD ribbon then replace HDD or Ribbon.
- If Seagate DB35.1, DB35.2，SV35 or Maxtor 17*g has compatibility problem. Please upgrade to the latest version to solve this problem.
- If Front panel error then replace front panel.
- If Main board is damaged then replace main board.