I have had it happen 2 or 3 times now. First time I found that the cable connection near the back of teh dash radio was caught down in the engine compartment pinched in the doghouse. No appearent damage, moving the wire fixed it.
Happened again, and I found that if I disconnect the wire (bnc type connector) near the back of the radio and plug it back in it worked.
I have yet to trace out exactly what the real problem o fix is.
I'm not positive, but I think the camera is powered through the signal wire by the radio unit in mine