A couple of times I have come to my PC to do something. wiggled the mouse to clear the screen saver and found that the system is unresponsive. I have blank blue screens on both monitors and no keyboard or mouse action will clear it.

Original solution was to reboot, although I have since discovered that Alt+Ctrl+Del will enable me to get to Windows 8 task manager and then to other screens.

It may be related but I also note that the screen saver is just a blank screen. I rarely get the graphic screen that describes the activity. That's no big deal as it's all gobbledegook to me but I wondered if it was significant?

Core i7 quad. 8GB RAM. Limited to 25% capacity to keep fans under control. Win 8.