My parents purchased a camera system more than a decade ago, and they called someone over to (do something with them? They don't remember...)
Anyway, the result was that almost all of the cameras went down.
They all have power, but there is no video stream from them. They light up with their infrared LED's at night, but after checking the DVR's settings, they have no video feed coming to the DVR (This was also checked by directly wiring the camera to a TV with no DVR in between them).
Additionally, I pulled one of the cameras down and brought it to my TV and gave it power (DC 12V from my power supply), and wired it directly to the TV (No DVR in between to rule out DVR issues).
It had no video feed.
Could all of the cameras have died over time (Which seems wildly implausible to me, they are exterior cameras), or am I missing something? My mom said that the person who was called over was adjusting the cameras physically and might have turned them off somehow, but upon inspection of the cameras, there is no such switch.
Here is the make/model of the camera: