Thanks again Enrique.
Had a look at the link.Sadly I understood hardly any of the offered solutions.
e.g: "Video Signal cable"?, " Change signal to a different port"? "Switching integrated video card"?, "UEFI"? , "BIOS"?
These are just a few of the tech items mentioned.
Sorry Enrique,I'm an intelligent bloke but the whole link might as well have been written in Ancient Greek for all I could understand of it.
I wouldn't presume on your kindness any further Enrique.I would hate to exhaust your patience.
After all the problem only occurs around once a week.Hardly a catastrophe.
I think I shall find a local computer chap and simply hand over the device,with a wad of euros,and say " fix this please!"
Life's too short to worry about "graphics cards"

.....actually I did know about the "Fast Start".I never have it activated.
Next time,I will try the "W+ctrl+shift+b" as you suggest ( even I can grasp that )
Thankyou again Enrique. JB