Vista - Cannot copy file in Vista

If I right-click in a directory and choose New | Text Document, or Word Document or ..., the file does not get created.

Nor can I copy a file within Vista.

So Vista's drop handler, if that is still the right term, is kaput.
Do not recall the last time I used right-click to create a file, so I do not know when it got broken.

I believe that I copied files on 19/20 June 2009.

Any ideas on how to fix?

It's working again!

1. As the Windows update had been run 24 June, I restored a backup from 23 June. Alas, problem continued.

2. I then restored a backup from 21 June. Alas, problem continued.

3. I know that I did a COPY/PASTE as recently as 19/20 June, so I then restored a backup from 16 June. Problem fixed!!!!!

I then updated KIS, problem still fixed!!!!!!
I then ran Windows update, problem still fixed!!!!!!!

Evidence is that something broke between the 16 and 21 June bckups, most likely on 20/21 June AFTER I did a COPY/PASTE on 19/20 June.

I am now backing up the system.

I guess that there could have been a virus that KIS did not detect.
Any other suggestions for cause of the problem?

When the backup is finished, I'll turn on Automatic updates in KIS.