I have two identical Dell Optiplex GX520 desktop computers. Both are running XP Professional SP2 with all updates. When leaving them alone for an hour or more, they both appear to go into "standby" mode. One of them will "wake up" when a key on the keyboard is hit; the other will not and I have to press the power button very quickly to wake it up. I'm a loss to explain why these are different. I've checked the POWER OPTIONS in both computers; they're identical and hibernation is turned off.