Thanks to you all for your replies.
I have always found that any running of McAfee products on my gateway laptop caused more chaos than it fixed, but have been carefull to 'disable' the active scan unless I'm checking my mail.
I have now taken to 'exiting' the McAfee Icon application from the toolbar, and that seems to disable the background program. Since then things seem more stable. I also noted a big improvement to game playing.
I will hold fire on pressing the 'Nuke the Hard Drive' button for a while and see how things go.
Thanks again.