either the CCM (Camera Control Module) or the cam itself.
if you see the back up lines but black screen, it may be JUST the cam itself.
if no backup lines and a black screen it could most likely be the CCM.
since you have an older model, the CCM and cams are the same in the armada for sure and possibly nissan/infiniti sedans of the same years (2006-2010) so sourcing a used system (is thats the way you want to go) may be easier.