New here - need some help.

[diev]

Hi everyone. I'm new here.
I need some help: I have Dahua XVR 1A08 cameras.
They were working fine, until for some reason now I see a black screen. Clarification: It does NOT say "no signal". It is as if there is signal, but the image is totally black.
Does anyone have any idea?

 

[TonyR]

Have you tried a different monitor or cable?
Are the cam's analog or IP?
Do you see video OK if you log into the NVR's webGUI with its LAN IP using a browser on a PC?