>>>but I am beginning to think that it may well be viral in origin as the problem still remains.
It does not surprise me, when I saw the first suggestion to run CHKDSK and SFC I thought that was a total waste of time (I nearly said so yesterday but did not want to be accused of being negative).
There have been cases reported where genuine copies of Windows have been highlighted as not genuine.
A search on "Windows is not genuine" may find some suggestions.
Here is one
http://support.microsoft.com/kb/2008385