I read the item as suggested and tried it out but it did not work. There is no battery fitted to my laptop, I use it on mains only and the no restart thing has been happening for only a few weeks - the laptop is a few years old.
I have just noticed during the latest restart attempt that when the laptop switches off, if I just press the power button to restart, the machine switches off again immediately. If I then give a longer press, the machine starts but only gets past the first logo screen (a few seconds) and then freezes on a black screen, there is no indication that the machine is switched on except for the number lock light.
The only way to reboot the machine is to unplug it from the mains, leave it for 10 or 20 seconds then it will boot as normal. Am I missing something here?