Go to the Main Menu-->Advanced-->Storage and check if there is the hard drive and its status is normal.
If there is nothing on the storage or the status is not normal, it means something is wrong.
Please try the troubleshooting methods below.
1. If the status is unformatted, click format to format the hard drive. Please note that all recording files on the hard drive will be deleted after formatting.
2. If the hard drive is not from us, please make sure your hard drive is for surveillance use, not for PC use. The type should be SATA. SATA2(3GB/s) or SATA3（6GB/s）is recommended, and We recommend 5400 RPM and the brand can be Dest digital or Seagate.
3. Open the cover of DVR/NVR. Uninstall and install HDD several times. Hers is the method: https://support.sannce.com/hc/en-us/articles/900000433303
4. Install the hard drive and put it close to your ear to check if you can hear some noise. One hour later, use hand to touch the hard drive to check if it is warm. If you can not hear any sound and surface of the hard drive is not warm, it can prove hard drive is not even powered up. Please share our results.
5. Unplug DVR or NVR from power and plug it again.
6. Restore DVR or NVR to factory settings.
7. Change another adapter to power on the DVR.
8. Change another DVR or HDD if you have.