Power management options change on their own

I have a Windows XP Media Center Edition and in my power management options I
customize the times I want my computer's monitor and hard disks to turn off.
I set the standby option on "Never" and the close the lid option on "do
nothing" as well. However, every once in a while the options will just change
on their own. The standby option will turn to "20 mins" and the close the lid
option will change to "go to standby." I apologize if this question has
already been asked but I haven't found it yet and this is really starting to
bother me. Thank you for your help.