Problem Solved
Daughter had downloaded Kazaa which installed, amongst many things, a program called wupdate.exe (spyware). This program was hanging and on PC shut-down was throwing up an error message.
Further investigation revealed that if I shut down wupdate.exe via Task Manager then there was no problem at all loading programs.
So, a bit of re-booting via safe mode, a bit of file deleting, registry pruning and removal from windows start-up routine via msconfig got things sorted.
Daughter has also been given a flea in the ear about downloading programs from the internet
and perhaps I should cost out 3 hours of my time as well.
Many thanks to all who replied
