You could well be right frostbit! However, thanks to help received here for which I am truly grateful - even though, to most of you who know what you're doing, it must all seem bl**dy obvious!
I followed your advice markjoy, thinking that what you were telling me to do was a sort of clean-up preparatory to running scandisk with auto repair etc which itself was to be in preparation for the W98 defrag utility. Well, within only a very few minutes, on its own initiative it started to run scandisk in its most basic manner and all went well and quickly then it went straight on to defrag and rushed through that so quickly that I wasn't present when it finished! I had been watching it scrolling down through lots of depictions of the files it was moving around so I'm convinced that it was going perfectly.
Now I find that it has decided that it wants to repeat the process automatically each day and won't, apparently, be dissuaded from that intention as there appears to be no box to untick so that I can do it manually( now that I know how to, thank you all!) whenever I think it appropriate. So frostbite's pessimism may well be justified!
There's no remedy for my ignorance, I'm afraid!