There are three levels of preset power management in Vista ... Balanced, Power Saver and High Performance ... You can find further reading in this Microsoft Article. I personally recommend that you actually customise the settings other than relying on any of the presets. None of them is exactly perfect for most systems.
To customise these settings to your own needs, follow these steps.
Open power options by simply typing Power Options in the search bar from the start button. Or, go the long way and, click the Start button / Control Panel / Hardware & Sound / Power Options. ;-)
Click the "Create a power plan" in the left pane.
Press Next to continue ...
I do NOT recommend enabling the "Put the computer to sleep" function.
Now press the Create button ...
As you can see, we now have our new power plan ready to further tweak. Now simply click "Change plan settings" to get to the more detailed settings
The setting you want is display....
Let me know if this works for you !!!!