Johnny45

I have a sentinent cctv system. It has 4 cameras. When i turned it on first it worked good. I turned it off and when i turned it back on a few days later it said "no signal" on the monitor. I cannot get a picture on it. Would anyone know how to sort this??? it goes to sleep after a few seconds. Thanks guys

all the connections are good. no problem with power to cameras. any more suggestions please??? Thanks