My system seems is running fine but today for no reason at all I clicked on
"Activate Windows". I expected to get a message that Windows was already
activated but instead I get the following:

C:\Documents and Settings\All Users\Start Menu\Programs\Accessories\System
Tools\Activate Windows.lnk
The NTVDM CPU has encountered an illegal instruction.
CS:0532 IP:06f8 OP:63 75 6d 65 6e Choose 'Close' to terminate the
application.

Can anyone tell me what this is all about and how I can fix it?
Thanks,
Al