Hello Chris, update on this. it was the power supply as thought, thanks for your help, changed supply all is back to normal friend happy
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The little switching power supply's for the cameras have a problem with voltage spikes on the AC mains, one spike high enough and they are toast.
I run all cameras to a single supply that is battery backed up and has voltage surge protection, or you can use a supply that will run all cameras and the DVR with a UPS system to protect them, this also allows the DVR and cameras to run when the AC power is out.
This also protects you from a burglar tripping the house main breaker to shut off the CCTV system.
The big problem with the IR night vision cameras is that at night the IR LED's can be seen, this gives away the fact that you have a CCTV system, to counter this I use a CCTV camera that does not have the internal IR LED's, then use some of these hummers to illuminate the cameras field of view.
No Red Glow 940nm IR LED Total Invisible Night Illuminator - ENC-900
Mounting these at the highest point of the roof keeps things out of reach for most burglars, they also run on 12 volts DC so a battery back up keeps them on when the power is out.