Thank you Txhamguy
Your very detailed reply is much appreciated.
Sadly it does not work for me.
When the problem first appeared a week ago there were blue screens with options available (I tried those but none worked)
Now the only blue screens are telling me that the update is in progress after which it all goes blank.
I have a black screen with the "C.... Desktop is unavailble" error message
and a partial task bar none of which works. There is no internet connection although the internet light shows positive
If I try ctrl - alt - delete and sign out but just goes round in a loop.
Windows +R works but using CMD I only get the user and not administrator privileges
so cannot follows Scannow or DISM
Windows +X does not work
Start does not work
I have managed to get Task Manager but have no idea how to use it
I can access BIOS
That is as far as I go for now. Tomorrow I shall go and buy a USB ready for any fix or for a clean install (reluctant to do this as I may lose what is on the computer)
Thank you again and for any further ideas
MrQ