Downloaded and installed fine, then tried to restart, it began to start windows and then stopped with an error message and a promise to fix it and start again. OK thought I just a slight glitch but it can fix itself
After several more attempts, with varying results but no startup, I decided that the only answer was the nuclear option of the dreaded recovery disc made when the computer was new. This wiped out all files and downloads made in the last four years
I have spent about 12 hours getting back to some semblance of normality, with a lot of shouting and swearing at the screen, and have still lost a lot of data, nothing of vital importance but inconvenient all the same.
The moral of the story is make a recovery copy to dvd at regular intervals
P.S. I have now downloaded the update that caused all the trouble (after making a disc ) and everything works fine
P.P.S. I know a lot about how computers work but not how to work them
P.P.P.S. This should have been in moans and groans (see above)