My goodness it was slow but it really looked as if it was going to work - my scandisk, preparatory to defrag, I mean. It got to 750,000 clusters (whatever they are) out of a total of 1,250,000 and then stopped, but completely. I waited for two more hours but it moved not one bit further.
I didn't want to restart from the beginning (as you might well imagine) but, with the faint hope that it might jump back fairly quickly to where it had got to, I did restart it. It didn't jump back over the stuff which had already been checked so I stopped it again.
I really don't want to spend more than thirty hours repeating the exercise only for it to stop again in the same place so i think I ought to try to tidy things up a little (eliminate .tmp and .chk files?) and go straight to a defrag.
Is it going to take a week? On another thread I see that the standard defrag (which made so little progress before) gets quite a good press if used with the advice which I have received here - i.e. in safe mode with the router disconnected and as much else turned off as possible. Do I go for it or is there really a better, quicker and less problematic product out there?