C600's reboot when shutdown requested.

I have suddenly had 3 users with C600's report that when they choose to shut down their Windows2000 SP4, their machine reboots as if they asked to restart.  These users have reported this behavior in the last month.  I've observed it at least once, so there's no "I accidently told it to restart when I wanted a shutdown" going on here.

 

I've looked through the last 6 or so pages of this forum and have found no similar posting.  The closest suggestion I found was to tighten the screws on the userside of the laptop.  I've tried that on at least one with no luck.  At least two of the machines, I've scanned for adware.  One found nothing (not even a cookie) but still reboots.  On the first reported one, I upgraded the BIOS but it still occasionally reboots upon shutdown request.

 

Has anyone else seen this behavior or does anyone else have a solution?