You have 3 things to consider. The back up camera itself, The wiring and the monitor. Replacing the monitor may not be the fix. Hard to tell without considering the other areas.
If another monitor works in place, it sounds like you've found the culprit. If the other monitor works completely normally, and you aren't even seeing menus on that monitor, AND the power button is blue (which normally indicates powered and in use), it sounds like the back light or some internal connection on that monitor is bad. Hope that helps and good luck!
As these are aftermarket kits, check the wiring as well all of the connections within it to ensure a good conductive path.
Corrosion and road debris often causes problems like this.
