'It can also be insufficient power. Verify the source of power and the rating requirements of the cameras. If they require 12v 500mA (just an example) then a 12v 2mA is fine for 4 cameras (once again, just an example, as it doesn't really sound like POE was used to power them). '
I used the switch at the back of the unit to power off/on the DVR record tried it a few times but that didn't make any difference to the issue. I decided to check out the power adaptor as you mentioned and disconnected the device to read the power settings afterwards reconnected as it seemed to be fine. I switched the device back on the cameras screens flashed with pictures and black screens four or five times and the picture steadied itself and seems to be working fine. I think disconnecting the power completely seems to have possibly reset the adapter and all is working fine. Thank you guys for all your advice and suggestions always something to bear in mind for the future.