If you don't find a noise problem, this is something you can try.
Do you only have one camera? If so, and if your using AHP/IWatchout setup another "dummy" camera within the same group of four. (cam1 is c1, dummy cam is c2) then try switching cams and see if that helps to get your video back. If that doesn't work you might try unplugging the camera and plugging it back in.
I have this problem every once in a while, a camera will just show flashing lines like it lost a signal. Normally switching cameras will straighten it out. Why it does it I don't have a clue though.
Another idea, is to unplug the va11/va12 and plug it back in. But be advised that doing this sometimes it will go through the driver install again.