Thank you for all of the excellent replies.
I hate to admit it but after checking the fuse to the thing I went back in to have another look at the monitor controls. There was a button that I had overlooked and sure enough, it was the standby/on button. Macantic nailed it much to my embarrassment.
(Please don't tell anyone).
I'm just learning this motorhome, I've only had it for 11 years.
Thanks again.
dreamer.