Many thanks to you Nightrider, Orac and Richard. I did as you suggested and, between them, they seem to have done the trick.
Trend Micro's Housecall found something called ''TROJ SMALL.J'' which it deemed ''not cleanable'' in C:/dload.exe*C:/dload.exe* - whatever that all means. It suggested that I delete it which I have now done and the 'startup' symptoms mentioned above seem to have gone away.
I am mystified why my Norton kit didn't find it on a full scan. Should I be changing provider perhaps?
Again, many thanks and happy landings - CFU tonight!!!
mcdhu