Windows' hibernate restarts computer

It used to work... Then one day it didn't. I clicked on Windows XP's Hibernate button in the Start, Turn off computer menu. The computer hibernates, and then restarts, instead of turning off.

To the Google machine! Hmm, I find a few other reports of people with a similar problem even in Windows Vista. Like these articles: Reboots from Hibernate - Flexbeta and Hibernate won't power off...it' restarts!. No solutions there.

I hadn't installed any new software or updated drivers, so those suggestions did not apply. I considered the USB tree, and tried unplugging some devices to see if they affected the reboot after hibernate. They didn't.

Then I eyed my APC Back-Ups... It uses a com port instead of USB. A week ago I had disconnected the battery because the UPS indicated it was bad. I could live with the UPS essentially being a surge protector, but it would beep insistently and long at random times. There is perfectly good error light on the unit which is labeled "battery bad".

Anyways, if you have read this far you deserve a solution. Unplug the UPS from the computer (or replace the battery). Problem solved and hibernate works. I plug the com cable back in and the reboot problem reappears.

My guess is the UPS is indicating that there is some kind of problem so the UPS service prevents a shutdown. It seems backwards since a hibernate would be safer than running on a UPS with a failed battery.

If you do not have a UPS, I would try the solutions in the links above, or look at your USB devices. In Windows' Device Manager, some devices allow you to check off whether it's safe to power them down, so a USB device could hold a system hostage that way.