problem and solution
When my computer was turned on, it worked fine, but it was important not to put it on standby or turn it off.
I thought it was the power button that was faulty, but it was actually the power supply that was the cause. I contacted LDLC and they recommended this power supply. The power supply has been changed and the computer works perfectly, including going into standby, switching it off and on again.
I have been using this product for some time now and it is a great product, well packaged and well priced.