Check that HDD is detected by NVR.
"Record Status" is set to, "Enabled" on all channels.
Check, "Record Schedule" and ensure your desired recording is enabled; Motion, Schedule, or Alarm Recording.
Recorded file has been overwritten.
File is in DAV format. Use Conversion Tool.
There are following possibilities:

If HDD ribbon is damaged then replace ribbon or HDD.
If HDD is broken then replace HDD.
If Upgraded program is not compatible then find another program to upgrade.
If the recorded file has been overwritten then there's not much you can do unless you have backup.
If Record function has been disabled then enable it.

HDD

Ribbon