Waking up the monitor

From time to time, when the machine has been unused for several hours, the monitor will go to black and the yellow sleep light. If I move the mouse, the yellow goes to the green active signal, but the monitor stays black. I can hear the machine apparently ready to work, but I can't get the monitor (a high-end NEC) to illuminate short of a reboot. Is there a key-stroke combo which might jar it into life, or at least reveal if the CPU is awake? I've told windows never to turn off the system, but I do have the screen go to black after 15 minutes of inactivity, and normally that works fine. But this occasional need to reboot is annoying, especially when I can hear the computer apparently ready for duty.
O.

 

As well as switching "Turn off monitor" to never in the power options, you may need to boot into the BIOS on startup, Del or F1 key and go into the BIOS power management and make sure any setting for monitor sleep or system standby is switched off.
I would also check for any later drivers for your video card as well.