Have a look in the Power Options section of Control Panel for available adjustments to Hibernate/Standby.
I recently reinstalled Win XP Home on my computer. About 3 weeks after this, the computer started going into "hibernation/standby" automatically after a brief period of non-activity. When this happens, hitting any key brings up the "user menu" and clicking on my name restores the computer to the ready mode.
While it's a bit of a pain, this is really not a bad thing if in being offline prevents any outside access to my computer. My question is "What is turning on this mode to revert to hibernation/standby?" I would like to setup my wife's computer to act the same way.
I realize that hibernation and standby are two different modes, but I'm not sure what actual mode I'm going into and hence my use of "hibernation/standby" above. I suspect it's standby since there is almost no waiting to the computer to come back up after clicking on my user name.