Thanks for all the help, it is amazing.
I tried the MB in a different computer case with its own power supply with the same result. I tested the power supply output and it is giving 4.8 volts on some of the outputs so it is working OK (I am pretty sure). I tried the power connector both ways and also varied the position on the board, also tried the reset switch in case they had the diagram wrong. This board is an ATX but it only uses one power connector from the PSU. I rang the tech support and they confirmed there was only one connection. They suggested I reflash the bios whicb I did, but I cannot see how the bios would give this problem. Would bad memory cause the board to fail to light up?
I suppose I must have fried it with static electricity or something, although I tried hard not to. I only use four metal screws to hold a board, and use plastic otherwise. I was advised that the metal connectors do not need to be insualted from the board, since the connector points are electrically isolated. Learning all the time.
But hey, thanks a lot.