Monitor Cutting Out

No idea why this happens as I have hibernation and sleep off, but if my computer goes unattended for 6+ hours, it will lock up. I'll come back to it and the monitor will appear to be "off", although on. I'll move the mouse, nothing. It's like it's asleep and won't wake up, but I have all sleep and hibernation modes disabled. My only solution is to do a hard boot. How can I prevent this and what is it? I am on Vista Home Basic x32.

 

I see the Power tab, but I don't see that particular option. Anything else?

 

Oh, I don't see or have this tab then. Also, this morning I noticed that when this happens, the power light on my case is yellow, not green. My monitor is off. When I move my mouse, my hard drive makes a short noise and the power light turns green, but the monitor stays off. Any idea?

 

What's the make and model # of your machine?

Often, the yellow vs. green light is an indication of some type of motherboard-induced state, such as S1, S3, WOL, etc.
You might try entering your BIOS setup and making sure nothing is enabled as far as power-saving or sleep modes.