Thanks for your inputs.
Simply deleted the 4.3 Gb file - neither Word nor Wordpad would open it - ran Defrag / Chkdsk neither of which showed any subsequent problem.
I then had to leave (now in New York and Atlanta for a few days) but I gather performance much improved.
Will have another look when I return - in the mean time no spyware identified (didn't have time for Adaware or Hijack).
Your inputs much appreciated.
Brgds
TimS