Occasionally, I will leave my PC idling until it goes to screensaver, or lock it with Windows+L, and then when I return to use it again it won't respond. The monitors receive a signal, and the keyboard's Num Lock/etc. keys toggle the corresponding indicators, but the monitors remain blank rather than displaying the lock screen no matter what buttons I press or how much I move the mouse. I tried plugging in another mouse during this period, and it received power, but moving it and pressing buttons was similarly ineffective.
I can't tell whether it's something to do with power settings (I set it to "performance," disabled USB selective suspend, all that stuff), or drivers, or my video card, or what. Next time it happens, I will attempt to check whether it's purely a display issue by pressing the necessary buttons to log in and play some audio. For now, I have turned off screensaver, monitor power-down, hard drive power-down... all settings related to reducing the computer's "on" state.
Ideally, I would like to know the actual cause of this and how to fix it. Alternatively, I would be happy with a solution/workaround that will let me leave my PC and come back to it a few hours later without having to hit the reset button and boot from scratch (when I Sleep the PC for several hours, try to wake it, cannot do so, and hit the reset button, it restores my Windows session, presumably because of some kind of hybrid sleep functionality that includes a hibernate).