Hibernation settings are also turned off. I checked the sleep settings and they are all turned off. This is a desktop computer, so not a battery issue. And yea users are always too busy so in general I just document that fact they won't let look at the computer and let the user know until they give you the time you need to test it you cannot fix it.
I would sent a bit of time watching the user while it happens. It could also be the user and not the computer. I would also check the scheduled task for possible things causing it.
If this is a laptop it could be a bad battery other then that as other's have said if it was hardware related it won't display the shutting down message.
My first thought is to check the screen timeout/sleep settings.
