Monitor doesn't wake up

Hi, when I move the mouse the monitor does not wake up, I have to turn off
using the switch and reboot every time this happens. I set it not to turn
the monitor off in the power settings, and also not to put the computer to
sleep. Still, if I turn the monitor off using its power button, I cannot
wake it up by moving the mouse, I have to turn the computer off. Please
help, this is the single most troubling problem I have with Vista, other
than that I like it and I have been able to find solutions to other problems
I had. Thanks a lot in advance..........John