Good News: Managed to speak to a Dell Tecchie in Bangalore. I had my desktop on and available to switch laptop to external monitor. He went through a series of keyboard combinations as diagnostic checks, during one of which the laptop screen flashed blue, green, bed, black, white in turn (I guess proving it is not the screen). At the end of the tests he concluded it was a faulty motherboard and said there have been other reports on this model. He promised an on site repair at my house as it is in warranty and I bought the premium service too.
There are no immediate replacements , so a "short" delay will ensue while the correct motherboard comes from origin ? China?. I hope it will be in a few days but suspect a lot longer. He said it will not affect my SSD hard drive or contents. Good job I have this desktop and an iPhone for e mail. Had this new, shiny expensive laptop been essential for a business I would have been in deep mire. Will update from time to time.