[dba-Tech] right-click closes Win explorer

I have just got a very unusual thing on my WinXP PC:
when I right-click a file in explorer, explorer closes
same happens when I mark the file and hit delete
(I can right-click a folder and get the menu as usual. this happens only on
files)

I have run AVG virus scanner with the latest update
and found no virus

have rebooted  - still doing it

I have downloaded a little utility (PC Mighty Max) which is supposed to find
problems in registry and many other places - it didnt find anything

anybody have any idea where to start searching?

oh, I did install a windows update, but I dont have SP2 installed yet.
I have also installed the update on a different machine and it doesnt show that
problem, so it might not be the update.

thanks for your help
Lembit Soobik