Restarts instead of shutting down

[Don]

This is a bit strange. My machine seems to work fine, but when I go to shut it down, it seems to shut itself off but then restarts spontaneously five to ten seconds later. The only way I can keep it shut down is to turn (effectively) yank the power cord while the machine is off (there's an off switch on the back of my case). Anyone have any ideas? Is there a log file I should post?
Thanks.

[SecretCode]

If you run the following command from Konsole, is it the same?

sudo shutdown -P now

-P indicates power off. If this doesn't result in a power down, it may be something in your firmware settings.

[Don]

Thanks for the quick reply. I'm sorry I couldn't get back sooner; I was away from the machine.
So I tried the command you sent me, and it did do a proper shutdown. That's great; I'd rather not have to flash the BIOS unless absolutely necessary.
Then I restarted and tried the shutdown command from the K menu. It, too, did a proper shutdown.
I suppose my remaining question is whether the command you sent me has some mystical healing qualities. If so, does it work on personal physical ailments, or just on computers.
Thank you so much for your help.

[SecretCode]

Now that you've mentioned the mystical healing powers ... you've broken the magic and it will probably fail again!